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A VETERINARY DISSECTION GUIDE 



■2.9-1- 



PART I 



The Joints, Muscles, and Viscera of tlie Horse 



BY 

SEPTIMUS SISSON, S. B., V. S. 

Professor of Comparative Anatomy in the Oiiio State University. 

Author of "A Text-Book of Veterinary Anatomy." 

Member of the American Association of Anatomists. 



Columbus, Ohio 
1911 






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PREFACE. 

This guide was prepared primarily for the use of students in the College 
of Veterinary Medicine of this University, and has been used with satis- 
factory results in the anatomical laboratory in the form of mimeograph 
sheets. It is now printed in response to the desire of several teachers, and 
in the hope that it may economize the time and energy of instructors and 
students, and conduce to orderly and thorough work in the dissecting room. 

It is perhaps hardly necessary to say that this manual is in no way 
designed to take the place of descriptive texts and atlases,* but attempts 
to state briefly and in orderly sequence the steps necessary to be taken to 
deal intelligently with the material under consideration. It is the belief 
of the writer, based on extensive experience, that the manipulations herein 
recommended will be found practicable and effective. It seemed desirable 
to interleave the guide with blank pages, on which notes and sketches 
might be made. 

The author is indebted to his associate, Dr. F. A. Lambert, for assist- 
ance and suggestions. 

Septimus Sisson. 
The Ohio State University, 
September, 1911. 



*The nomenclature used in this guide corresponds to that of the Author's- 
" Text Book of Veterinary Anatomy," published by Messrs. W. B. Saunders Co., 
925 Walnut Street, Philadelphia; and the marginal numbers refer to figures in that 
text. 



INTRODUCTION. 



Sound anatomical knowledge is very largely a product of thorough and 
intelligent work in the laboratory. All other methods of instruction .and 
study are to be regarded as accessory to direct observation. The knowledge 
of the various structures that is essential to the professional student is 
mainly a matter of visual memory ; the practitioner of medicine and surgery 
must be able to re-visualize clearly and accurately what he saw in the 
dissecting room. The power to do this varies greatly, depending very 
much on previous training. In many cases unfortunately the student 
finds that his ability in this respect is very limited and must be cultivated 
assiduously. It is evident that two conditions must be fulfilled in order to 
meet practical requirements. First, the parts to be observed must be 
clearly visible in every detail, so that a sharp definite mental picture is 
obtained. The work then must be clean, thorough and methodical, the 
various structures perfectly exposed, and the preparation in general such 
that the dissector need be in no way ashamed of it. The student will find 
that the acquisition of ordinary dissecting technique will occupy most of 
his time at first, so that he must proceed very slowly. Accurate and thor- 
ough dissecting is not only indispensable in anatomical study, but is also 
admirable training for clinical work. Dexterity in the use of those instru- 
ments which are most commonly employed in surgery should be acquired 
in the dissecting room. But the mechanical side of the work, important 
as it is, is the means, not the end. As the structures in a given region 
are exposed they must be carefully observed, their names learned, and 
their form and relations examined. The amount of time required for this 
will vary with the simplicity or complexity of the region and with the 
individual. The dissector must satisfy himself that he has seen thoroughly 
aU that is to be seen before he proceeds further, since no clear and lasting 
impression will remain in the mind unless this is done. Sketches of dissec- 
tions, even though of a rather primitive character, are of great value in 
fixing anatomical relations in the memory. 

It is customary for two students to work together on a part ; in dealing 
with large animals, such as the horse and ox, raany manipulations require 
the co-operation of two dissectors. It is essential that each do his share 
of actual dissecting ; the possession of greater skill or liking for the work on 
the part of one collaborator must never be allowed to interfere with his 
partner participating duly in the procedure. 

Students should accustom themselves to exhaust their own resources 
before calling on an instructor for information or assistance. Self reliance 
and ability to deal with new and unforseen situations are needed nowhere 



more than in the practice of medicine and surgery. On the other hand, 
vuuisual difificulties, doubtful points, aiid variations from the usual arrange- 
ment should be brought to the attention of an instructor without hesita- 
tion. In this way the energies of instructors can be conserved and utilized 
for the best interests of the students and for th^ advancement of anatomical 
knowledge. 

In beginning the dissection of a region examine all superficial features. 
Many bony prominences can be recognized by inspection or palpation. 
Study a figure of a superficial dissection, and see how much of what is shown 
in the illustration may be made out more or less clearly on the part before 
dissection. Study the region in the living animal. 

CARE OF PART. 

As soon as a part is assigned the dissectors take charge of it. Care 
must be taken that it is not allowed to dry, as this absolutely prevents 
good dissection. The face and lower parts of the limbs .are to be 
wrapped with moist cloths at all times when they are not being worked on. 
Students must not interfere with parts belonging to other dissectors without 
the permission of the latter. Due diligence is to be observed in carrying 
on the work, so that material will not spoil on account of unnecessary 
delay and lack of attention. Do not uncover more surface than you need 
to work on in the time immediately available. When ceasing work 
endeavor to replace all parts in their natural position; this not only helps 
to keep the material in good condition, but may be made a means of fixing 
facts in the mind. Keep your part and table clean. Place all scraps of 
tissue in the receptacles provided for that purpose 

INSTRUMENTS. 

Most of the dissecting sets as made up for sale are cheap and unsatis- 
factory. It is better to assemble what is required. (1). It is advisable 
to have three knives. Of these two should be high grade scalpels, of the 
type known as minor operating knives, with convex edges ("bellied") ; the 
best lengths of blades for veterinary use are 1^ inches and 2 inches respec- 
tively. The third is a cartilage knife to be used for rough work, cutting 
about bone, etc., thus enabling the dissector to avoid damaging his better 
knives. (2). The dissecting forceps should be of large size, with properly 
grooved points which hold well. (3). A pair of straight scissors, medium 
size, with both points blunt, are very useful for working in comers, remov- 
ing fat, etc. (4). One or two double hooks are necessary for fastening 
back flaps or structures which have been reflected from the field of opera- 
tion. They are much more satisfactory than chain hooks. (5). A 
dissecting probe of the sort introduced by Professor Mall is very convenient 
for following the finer branches of vessels and nerves. (6). A blunt 
probe and a blowpipe are necessary for working out ducts, inflating hollow 
organs, etc. 



Chisels, hammers, saws, bone forceps and the Uke arc included in the 
laboratory equipment. These arc to be returned to their jjropcr ])lace as 
soon as they arc done with. 

In order to do good work knives must be kept sharp, and a i)roper 
whetstone must be constantly at hand in the dissecting room. A rather 
quick-cutting stone which can be used with water is the most practical; 
probably the best is a yellow Belgian hone, but an India or a iine car- 
borundum stone i« satisfactory. When a knife can no longer be sharpened 
properly by this means it needs to be ground. 

Instruments should be cleaned at the close of the laboratory period. 

In dissecting, the scalpel is held usually Hke a pen, short and accurately- 
gauged strokes being necessary. In making long incisions, however, the 
knife is held *'in the fist," and in cutting through firm and resistant 
structures this method is also used. Precision in the use of the scalpel 
^ould be dihgently cultivated, and the resistance of the various tissues 
carefully noted. 

CLOTHING. 

A long, sleeved apron or an operating gown affords sufficient protection 
to the ordinary clothing in dissecting properly preserved subjects in a well- 
equipped and sanitary laboratory. 



DISSECTION OF THE HEAD AND NECK. 

VENTRAL REGION OF NECK AND SUBMAXILLARY SPACE. 

Can you find the submaxillary lymph glands ? Locate the facial vessels 
and parotid duct as they turn around the lower border of the ramus of the .„ 
mandible. Is the ventral edge of the ramus in front of these thick or thin? ^2 

In the middle line feel the body of the hyoid bone. The body of the 
thyroid cartilage of the larnyx may be felt more or less distinctly a little 
further back. The arch of the cricoid cartilage can be located. Passing 
fxirther back note where the trachea is distinctly palpable. Find the end 
of the cariniform cartilage. 

Examine on either side the jugular furrow and vein. Gauge the thick- 
ness of the skin ; is it closely adherent to the underlying parts ? 

Make an incision through the skin in the ventral median line from the 
body of the mandible to the cariniform cartilage. This ^^ill be continued 
bacla\^ard by the dissector of the pectoral region. Reflect the skin (and 
only the skin) far enough to expose .the lower border of the jaw and the 
jugular, furrow. 

Examine the superficial fascia and the cervical part of the panniculus 185 
camosus. 

Incise these along the median line and reflect them laterally. The 
panniculus is closely adherent to the mastoido-humeralis near the shoulder. 

Clean the surface of the omo-hyoideus and stemo-cephalicus in so far 
as these muscles are accessible. 

Cut the panniculus across near its attachment to the sternum. 

Clean the jugular furrow, exposing the jugiilar vein. 

Flex the neck so as to slacken the muscles here, and clean the deep face 
of the stemo-cephalicus and (as far as possible now) the omo-hyoideus. 

Clean the stemo-thyro-hyoideus and the ventral surface of the trachea. 
Find the intermediate tendon of the former and the division of the muscles 
into thyroid and hyoid branches. Do not cut any of these muscles. 

Note the position of the carotid artery. The vago-s}Tnpathetic nerve 
trunk lies on the dorsal surface of the artery, and the small recurrent 
nerve on its ventral face. Examine the oesophagus. 

If any part of the parotid gland is uncovered, clean its surface, taking 
care however to save the duct and the parotido-auricularis muscle. 
FoUow the duct and the external maxillary vessels in the submaxillary 
space. 

Clean the mylo-hyoideus muscle, and the anterior belly of the digas- 
tricus and its tendon of insertion. Note in doing so the submaxillary 
Ijnnph glands, which may be removed. 

After the subject is suspended review the ventral muscles already 
dissected. 

1 



LATERAL REGION OF NECK. 

Rcmoxc the skin from the lateral surface of the neck. Examine and 
remo\-c the suj^erficial fascia and the panniculus camosus. This is a 
procedure which requires much care to avoid injury to the trapezius 
cerxncalis. Note the course of the large spinal accessory nerve. 

Clean the connective tissue and fat off the funicular part of the liga- 
jyg mentum nuchae. 

Clean and examine the trapezius and mastoido-humeralis. 

Remove the fascia from the splenius and scrratus cervicis in so far as 
these muscles are exposed at present. 

In conjunction wdth the dissectors of the withers cut the trapezius 
179 across about a handbreadth from and parallel to its origin and reflect the 
flaps. Clean the fascia off the muscular surface now exposed. 

Dissect up the rhomboideus from the splenius. Study its orgin; the 
insertion cannot be seen at present. Cut the muscle across about a hand- 
breadth in front of the scapular cartilage. 

Clean the deep face of the mastoido-humeralis and dissect its vertebral 
digitations. Cut these digitations across, lea^dng good-sized sttutips 
attached to the vertebrae for review later. 

Clean the lower part of the splenius and the serratus cers^icis and sepa- 
rate these muscles. 

Clean the scalenus. Note here the roots of the phrenic nerve crossing 
the surface of the muscle. The brachial plexus appears a;s a flat band 
between the upper and lower parts of the muscle. 

After the removal of the thoracic limb examine the entire serratus 
magnus. 

In collaboration with the dissectors of the thoracic wa;ll, turn down the 
serratus magnus to its vertebral and costal attachment. Cut the muscle 
across a little above this attachment. 

The splenius is now to be studied and the dorso-scapular ligament 
examined. 

Cut the splenius across a short distance from its upper attachment atid 
reflect both parts. 

This uncovers the complexus, the trachelo-mastoideus, and the cervical 
part of the longissimus. Clean and separate these muscles, and examine 
them. Note the way in which the complexus passes between the two 
di\nsions of the longissimus. (The dorsal division of the longissimus = 
spinalis and semi -spinalis) . 

Clean the deep face of the complexus as far as convenient at this stage, 
and examine the structure and cervical attachments of the muscle; it is 
advisable not to dissect the poll till later. Cut the complexus across at 
the fifth cervical vertebrae. 

Clean the lamellar part of the ligamentum nuchae in so far as it is 
exposed. The superior or deep cervical artery lies on the ligament. 



Clean the niultifidus and separate its bundles. Examine the attach- 
ments of the lamellar part of the ligamentum nuchae. 180 

Clean and examine the intertransversalcs. 

Clean the rectus capitis anterior major as far forward as the wing of 
the atlas; also the longus colli as far as practicable now. 

Separate the head and part of the neck by cutting the soft structures 
as far as possible and sawing through the fifth cervical vertebra. 



THE POLL AND AURICULAR MUSCLES. 



172 



The term poll is applied to the atlanto-occipital region, but is generally ^"^^ 
restricted to the dorsal structures. It is bounded in front by the occipital . 
crest and laterally by the edges of the wings of the atlas; these can be felt. 554 
There is no natural posterior limit. 

In removing the skin here great care is necessary to avoid damaging 
the thin auricular muscles and the aponeurosis of the splenius. Incise 
the skin medially as far forward as a line connecting the internal canthi of 
the eyes, and make a transverse incision along this line. Leave a strip of 
skin about an inch wide around the orbit. Reflect the flaps very carefully 
as far outward as the zygomatic arch and the edge of the wing of the 
atlas, making a circular incision around the base of the ear. Strip the skin 
off the convex surface of the conchal cartilage. 

Dissect the auricular muscles — a procedure requiring care and patience. 
One dissector must hold the ear in such a way as to tense the muscle which 
is being cleaned by the other. Superficial muscles may be cut across 
where necessary in order to expose those which they cover. 

Pull the ear outward and backward and clean the scutiform cartilage 
and scutularis muscle. Note that the scutulo-auricularis superficialis 
superior is in reality a slip derived from the scutularis. 

Draw the ear baclavard and a little inward and dissect the anterior 
auricular muscles 

Expose the two superior auricular muscles by incising the cervico- 
scutularis and interscutularis an inch from the sagittal crest and reflecting 
the flaps. The scutulo-auricularis superficialis superior may be divided to 
expose fully the scutulo-auricularis superficialis accessorius. 

Draw the ear outward and forward, and clean the cervico-auricularis 
superficialis. Dissect up the muscles carefully, exposing the insertion of 
the parieto-auricularis and the cer\'ico-auricularis profundus major. 
Carefully remove the fat about the base of the ear here. The superficialis 
may be cut across to expose fully the profundus majo'r, and the latter in 
turn divided to expose the profundus minor. Pull the ear forward and 
dissect up the parotid gland to see the insertion of the profundus minor. 

Dissect the skin off the parotid gland sufficiently to uncover the entire 
parotido-auricularis. 



/ 



180 



Pull the car outward and downward, cxposini^ the eminentia conchae 
and the deep face of the scutiform cartilage. Dissect away the fat here 
and clean and separate the two deep auricular muscles. 

To find the tra^cus, divide the i)arotido-auricularis and zvKomatico- 
auricularis, and dissect the parotid <^land carefully off the base of the ear. 
The annular cartilage and the lower j^art of the conchal cartilage can now 
be examined. Note the connection of the styloid ]3rocess of the latter ^\^th 
the gvittural pouch. Remove any fat which remains about the base of the 
ear. Examine the scutiform cartilage. Replace the muscles and review 
them. 

Sever the origins of the posterior auricular muscles, and turn them and 
the ear forward. Clean the funicular part of the ligamentum nuchae. 

Identify the stumps of the splenius and mastoido-humeralis. Clean 
the anterior part and the thin aponsurosis of these muscles. -Blended \\ith 
this aponsurosis is a strong tendon attached to the wing of the atlas. 

Turn down the splenius from behind and above, separating it from the 
ligamentum nuchae. Clean its deep face and note that a digitation of the 
splenius is attached to the atlantal tendon just mentioned, but that the 
tendon may properly be regarded as belonging to the ventral part of the 
trachelo-mastoideus. The anterior digitation of the splenius is attached 
in part in common with the dorsal part of the trachelo-mastoideus. 

Dissect up the mastoido-humeralis from below, separating it carefulh^ 
from the omo-hyoideus. A digitation arises from the atlantal tendon of 
the trachelo-mastoideus. 

Sever the digitations of the splenius and mastoido-humeralis from the 
atlantal tendon of the trachelo-mastoideus, and follow the aponeurosis of all 
three to the cranial attachment, dissecting up the parotid gland as much 
as necessary. 

Cut the dorsal part of the trachelo-mastoideus across at the posterior 
border of the wing of the atlas, and turn the anterior stump forward 
together with the splenius and mastoido-humeralis. 

The anterior part and the tendon of insertion of the complexus are 
exposed. Clean these and separate them from the ligamentum nuchae. 
Cut the muscle across in front of the digitation which arises from the 
articular process of the third cervical vertebra, and reflect the anterior 
stump to its insertion. 

Clean the obliqui capitis and examine them. 

The rectus capitis posterior major lies alongside of the funicular part 
of the ligamentum nuchae. Can you separate the muscle into superficial 
and deep parts, dissecting from without inward? Separate the muscle 
from the ligamentum nuchae, cut it across in its middle, and reflect the 
stumps. Cut the ligamentum nuchae across in front of the spine of the 
axis; note the appearance of the cross-section, and reflect the anterior 
stump. Do you find the supra-atloid bursa? Is there evidence of disease 



( 



here in your specimen? If so examine a normal specimen if one is available. 
The rectus capitis posterior minor lies in part beneath the bursa and is 
to be cleaned 

Cut the obliqui capitis across and reflect the flaps. 

Complete the dissection of the ligamentum nuchae. 

The dissection of those ventral muscles of the neck which are attached 
to the ventral arch of the atlas and the base of the cranium cannot be 
completed at present, but the stemo-cephalicus, omo-hyoideus, and 
stemo-thyro-hyoideus are now to be worked out to their insertions if 
this has not been done. 

MUSCLES AND VISCERA OF THE HEAD. 

Remove the skin from the masseteric region. Note the facial nerve 172 
and its branches crossing the masseter muscle. Do you observe an}- 
pannictilus fibres? Clean the muscle and the parotid gland. In doing so 
be careful to preserve the origin of the small zygomaticus muscle. Do not 
dissect at present beyond the anterior border of the masseter. 

Study the parotid gland and follow the duct to the point where it turns 
around the lower border of the ramus. Note the jugular and external 
maxillary veins in relation to the gland and retain them. The gland was 
partially dissected up previously; complete this carefully, endeavoring to 
avoid damaging underlying structures. The tendon of the stemo-cephal- 
icus passes between the parotid and the submaxillary gland, and a thin 
aponeurosis connects this tendon with that of the mastoido-humeralis ; 
these are useful in separating the two glands here. 

Clean the submaxillary (salivary) gland in so far as it is now exposed. 

Clean the stylo-mandibularis muscle. 

Clean the temporalis muscle and remove the orbital fat. 

The pterygoid muscles and the digastricus are to be examined later 
after removal of the ramus of the mandible. 

Before proceeding with the dissection of the muscles of the cheek, lips 
and nostrils, study and examine the lips and nostrils. Explore the so-called 
"false nostril" and the nasal diverticulum. Palpate the alar cartilage. 
Find the external orifice of the naso-lacrimal duct. Locate the infraor- 
bital foramen, the naso-maxillary notch, and the anterior end of the 
nasal bones. 

The remainder of the skin of the face is to be removed with great care; 
take no fascia with it, and leave a strip about an inch wide around the 
lips and nostrils. 

The branches of the facial nerve may be removed with the fascia which 
partially conceals the muscles. Refer previously to illustrations of super- 
ficial dissections to avoid damage to the thin muscles. What is the nature 
of the facial panniculus? 

Clean and define the zygomaticus. 



Note the facial vessels and parotid duct passin^^ upward in front of the 
massctcr muscle. Clean these and follow the duct to its termination. 

Clean the levator nasolabialis and define its two branches, between 
which the dilatator naris lateralis emerges. Clean the nasal expansion of 
the latter muscle and work backward to its origin. 

Clean the buccinator and depressor labii inferioris in so far as they are 
now exposed, and follow the tendon of the depressor to the lower lip. 

The levator labii superioris proprius is partly concealed by the levator 
nasolabialis. Cut the branches of the latter across and reflect the posterior 
part. Clean the levator proprius and dissect its tendon to the common 
terminal expansion. 

Pass the forefinger back into the nasal diverticulum and raise the latter 
by bending the finger. Now dissect up the blind pouch carefully from 
behind forward. This exposes at the naso -maxillary notch the outer 
surface of the nasal mucous membrane and muscle fibres covering the 
bony margins of the notch. The thin muscular layer on the upper margin 
is the dilatator naris superior; clean it carefully, drawing the tendon of the 
levator labii superioris proprius aside. The dilatator naris inferior, which 
covers the nasal process of the premaxilla, is much thicker; clean it and 
determine its chief insertion. 

Examine an illustration of the alar cartillages of the nostrils, and 
346 determine their form and arrangement by palpation. Clean the exposed 
surface of the dilatator naris transversus. 

Determine the action of the nasal muscles. Slit the external wing of 
one nostril and the outer wall of the nasal diverticulum. Remove the 
mucous membrane from the naso -maxillary notch. Note the alar fold 
and its connection with the cartilaginous prolongation of the inferior 
turbinal bone. What muscle is attached to the cartilage? 

Expose the alar cartilage of one side at least and study its form and 
attachment. 

Remove the skin from the lips, exposing the orbicularis oris. The 
incisivi are best seen by everting the lips and removing their mucous lining. 

Remove the skin of the eyelids, and examine the muscles thus exposed. 
Only the tendon of insertion of the levator palpebrae superioris is seen 
at present. 

Cut the masseter across just below its origin and reflect it. Note its 
structure and remove it from the ramus. The posterior part of the 
buccinator and depressor labii inferioris are now exposed and are to be 
463 cleaned. In doing this observe the two peculiar veins which He along the 
borders of the muscles and note their connection with the facial vein. The 
upper one is the buccinator vein. Clean the fat off its posterior part and 
follow it around the maxillary tuberosity to the point where it passes 
through the periorbita. The lower vein is the vena reflexa ; it is continued 
on the inner surface of the ramus as the internal maxillary vein. The 
veins may now be removed. 

6 



1 \ 



The superior buccal glands lie on the upper part of the buccinator; they 
consist of small lobules of a pale yellow color. 

The bulk of one ramus of the mandible is now to be removed. Slit 
the cheek lengthwise; reflect the flaps, and find the orifice of the parotid 
duct. Lay the head with its ventral face upward and separate the soft 
structures from the inner surface of the ramus. It is not advisable to do 
this before you have had the procedure demonstrated by an instructor. 
It must be done with a large knife, the blade of which is to be kept on the 
ramus. Sever the attachments of the internal pterygoid and stylo-man- 
dibularis from the ramus. Then pass the knife blade along the inner 
surface of the horizontal part of the ramus, keeping it on the bone, and 
severing the soft tissues here. The separation must extend up through 
the floor of the mouth. Saw through the ramus (a) near its junction with 
the body, and (b) a little below the articulation with the temporal bone. 
In doing this take care not to damage the underlying structure; it is best 
to saw partly through the bone and finish the separation with a chisel. 
Remove the part of the ramus thus isolated but retain it for future 
reference. 

The cut surface of the pterygoideus internus, which was attached to 
the broad part of the ramus, is exposed; behind it is the stylo-mandibularis ; 
in front of it is the mylo-hyoideus. Along the lower part of the mylo- 
hyoideus is the anterior belly of the digastricus. Clean these muscles and 
locate their attachments to the part of the ramus which is removed. The 
lingual nerve crosses the pterygoideus internus and dips under the mylo- 
hyoideus. 

The pterygoideus extemus is deeply placed. It extends from the lower 
part of the pterygo-palatine fossa backward to the condyle and neck of the 
mandible. Raise up the stump of the ramus to see the insertion of the 
muscle, and if necessary remove part of the bone with pincers. 

Dissect up the pterygoideus internus carefully to its origin and cut it 
off short. In doing this endeavor to avoid injuring the very thin guttural 
pouch by raising the muscle and pushing the pouch off its deep face with 
the finger or scalpel handle. 

Raise the ventral end of the stylo-mandibularis and separate it carefully 
from the underlying structures. Note that the posterior belly of the 
digastricus is blended with this muscle, and must also be dealt with now. 
The duct of the submaxillary gland is to be found when cleaning the 
intermediate tendon of the digastricus. 

Clean and examine the submaxillary gland. 

The occipito-hyoideus muscle blends with the origin of the stylo-man- 
dibularis ; it fills the space between the upper end of the great comu of the 
hyoid bone and the paramastoid (or styloid) process. 

Cut the digastricus across close to its junction with the stylo-man- 
dibularis ,and cut the latter off close to its origin. 



242 



436 



The stylo-hyoidcus lies behind the great comu. Clean it and note its 
attachments. Observe at its insertion the pulley for the intermediate 
^endon of the digastricus. 

The external carotid artery passes forward under cover of the upper 
part of the submaxillary gland, emerges between the stylo-hyoideus and 
the great cornu, and crosses the latter. It is continued across the inner 
surface of the neck of the mandible as the internal maxillary artery. 
Look along it for the pharyngeal lymph glands. 

Open the guttural pouch in front of the great cornu and explore it 
thoroughly and study its relations. Pack the sac so as to retain its shape 
approximately. 

The large hypoglossal nerve is seen running downward and forward 
over the guttural pouch, the external carotid artery, pharynx and larynx. 
It disappears under the mylo-hyoideus, and is the motor nerve of the 
tongue. 

Close behind or partly under the great cornu is the much smaller 
glosso-pharyngeal nerve. 

The external maxillary artery has a somewhat similar course but 
passes to the submaxillary space. The large branch from it that is visible 
for a short distance behind the great comu is the lingual artery; it passes 
under the hyo-glossus. 

LINGUAL MUSCLES, TONGUE, ETC. 

Remove the external maxillary vein and the anterior belly of the 
digastricus, and examine the outer surface of the mylo-hyoideus. Reflect 
the muscle downward to the median raphe, and clean the structures thus 
exposed. Find the submaxillary duct. The lingual and hypoglossal 
nerves are to be observed and then removed so far as they are in this layer. 
436 Clean and examine the sublingual gland. Find the ducts and observe 
the papillae on which they open. Dissect up the gland from below and 
trace the submaxillary duct. 

Dissect the mucous membrane up on the side of the tongue until it 
242 becomes firmly attached to the underlying muscle, and remove as much 
as you have detached. Clean the stylo-glossus and note its form, position, 
and attachments. Cut it across about two inches from its origin. Reflect 
the posterior stump, and dissect up the anterior part from below upward 
till it blends with the intrinsic musculature of the tongue. 

Clean and examine the hyo-glossus. Raise its anterior border, cut 
the muscle across at right angles to its fibres and reflect the flaps. The 
lingual artery is exposed and may be removed. 

The small kerato-hyoideus muscle occupies the space between the lower 
part of the great comu and the small and thyroid comua of the hyoid bone. 

Note the triangular space between the kerato-hyoideus below, the 
phargyngeal muscles above and the root of the tongue in front, in which 

8 



there is no muscular layer. Pass the finger along the lateral wall of the 
fauces and feel here the series of rounded elevations caused by masses of 
lymphoid tissue, representing a diffuse tonsil. 

The genio-glossus has been exposed by the reflection of the stylo-glossus 
and hyo-glossus. If its tendon and lower edge is raised it will be seen that 
the median plane has been reached ; here there is a thin layer of connective 
tissue and some fat, which separate the right and left muscles. 

The genio-hyoideus lies along the lower edge of the preceding, in contact 
with its fellow of the opposite side. 

Replace the muscles and review them. 

PHARYNGEAL AND PALATINE MUSCLES. 

Cut the stylo-hyoideus across about an inch below its origin and reflect 
the lower part. Dissect the guttural pouch from below upward off the 
wall of the pharynx. 

The pharyngeal fascia covers the muscular layer. Note the thick part 
which extends from the pterygoid bone to the great comu. Remove 
the fascia. 

Find the stylo-pharyngeus muscle arising from the deep face of the 
great cornu where the latter reaches the lateral wall of the pharynx. With 
bone forceps divide the great comu just below the origin of the muscle, and 
also near the junction with the small comu. 

The pharyngeal muscles can now be completely cleaned and examined 242 
in the order given in the text. After theyjhave-breen- studied superficially 243 
the constrictors may be divided to expose the posterior part of the palato- 
pharyngeus and pterygo-pharyngeus. 

The anterior part of the last named muscles is crossed by the tensor 
palati and levator palati, which lie along the outer surface of the Eustachian 
tube. The tendon of the tensor can be followed to the humulus of the 
pterv^goid bone but not further at present. The levator is internal to the 
tensor along the Eustachian tube, and then turns down in the pharyngeal 
wall. The azygos or palatine muscle is to be examined later. 

ISTHMUS FAUCIUM, PHARYNX, LARYNX, ETC. 

Depress the root of the tongue and explore the isthmus faucium; what 
are the boundaries? Cut the anterior pillar of the soft palate and extend 
the incision backward and downward through the lateral wall of the 
fauces just below the soft palate. Slit the lateral wall of the pharynx just 
above the soft palate. The isthmus faucium, the soft palate, and the 
cavity of the pharynx are now to be fully examined. Study in this con- 
nection the illustration of a sagittal section of this region. Note the rela- 
tion of the posterior pillars of the soft palate to the entrance to 
the oesophagus. 



Dissect off the oral mucous membrane of the soft palate together with 
the thick underlying glandular layer. The aponeurotic layer is exposed. 
Follow the tendon of the tensor palati to this layer. Find the azygous 
or palatinus muscle. 

Study the position and relations of the larynx. Examine the aditus 
laryngis, and note its relation to the cavity of the pharynx and the isthmus 
faucium. Does the pharynx commui>icate with the mouth in the present 
state of the parts? If not, how is comraunicatdon established? 

Sever the attachments of the pharyngeal muscles from the laryngeal 
cartilages and examine the latter so far as they are now exposed 

Place the preparation with its ventral surface upward. 

Dissect up the stumps of the omo-hyoidei and sterno-hyoidei to their 
insertions and cut them off short. Deal likewise with the the stemo- 
thyroideus. 

Clean and examine the thyro-hyoid muscle. The ventral surface of 
the larynx which is exposed between them is also to be cleaned. Identify 
the body of the thyroid cartilage and the arch of the cricoid. Note the 
interval between the former and the body of the hyoid bone ; clean out the 
fat in this space., The arch of the cricoid cartilage is largely covered by 
the crico-thyroid muscles. 

Remove the fascia from the ventral and lateral surfaces of the trachea. 
In doing this look for the isthmus of. the thyroid gland. Examine the 
thyroid; are the lateral lobes symmetrical in size and position? 

Clean the oesophagus and the carotid artery. What nerves lie above 
and below the artery? What is the position of the oesophagus? Where 
and how does it change its position? 

The tongue, part of the hyoid bone, pharynx and soft palate, the larynx, 
and the trachea and oesophagus are now to be removed together for 
further study. Lay the preparation on its side. Cut the trachea and 
oesophagus across about a hand's length behind the larynx. Pull them 
downward and dissect them loose from the overlying structures. Complete 
the separation of the guttural pouches from the pharynx. Carefully 
separate the (previously undissected) lateral surface of the pharynx and 
larynx from the adjacent structures. 

Divide the stylo-pharyngeus muscle. Cut the pharynx across below 
the Eustachian openings, and divide the soft palate in a similar direction 

Depress the root of the tongue and divide the anterior pillars of the 
soft palate. Disarticulate the intercomual joint of the hyoid bone. Cut 
the attachments of the geno-hyoidei and genio-glossi to the mandible. 
Pull the tip of the tongue out of the mouth, cut the frenimi linguae, and 
separate the tongue from the mylo-hyoideus, cutting the mucous mem- 
brane along the line of reflection from the tongue to the muscle. 



10 



Study the form and structure of the tongue. Wash and examine the 240 
mucous membrane. Make and study cross-sections of tip, body, and root. 241 

Examine the part of the pharynx and soft palate which you have ^® 
removed. What is the pharyngeal isthmus? Slit the soft palate, the 
junction of its posterior pillars, and the first few inches of the oesophagus 
medially. Study the floor of the pharynx and the aditus laryngis as 355 
seen from above. 

Note the thick glosso-epiglottic fold extending from the base of the 
epiglottis to the root of the tongue. Incise the mucous membrane here 
medially, reflect the flaps, and clean the hyo-epiglottic muscle. 

Examine the structure of the oesophagus. How is it connected with 
the pharynx and larynx? 

Separate the oesophagus, pharynx, and soft palate from the larynx and 
hyoid bone. Dissect the external muscles of the larynx on both sides. It 
is necessary, before doing so, to study the cartilages, referring to illustra- 349 
tions of them. You can obtain a dissected specimen of the cartilages by 
asking an instructor for the loan of one. Do you observe any difference 
between the right and left muscles? If so, is the aditus largyngis un- 
symmetrical? 

Cut the muscles off one side and remove the greater part of the lamina 
of the thyroid cartilage on the same side. Is the cartilage partly calcified? 
Find the lateral ventricle and pass a finger back into the laryngeal saccule ; ^^^ 
note the extent of the saccule and its relation to the muscles here. 

Dissect the thyro-arytenoideus and crico-arytenoideus lateralis. These 
muscles will be atrophic (on the left side) if the animal is a ''roarer. " 

Examine the cavity of the larynx. It may be divided in the dorsal 
medial line and the two sides pulled apart for this purpose. Is the cricoid 
partly calcified? How is it connected with the trachea? 

Examine the joints and ligaments. Separate the cartilages and clean 
and study them. Study the structure of the trachea. 

A review should now be made of the muscles of the parotid region and 
the inner surface of the ramus as seen from the inner side; this refers 
particularly to the occipito-hyoideus, stylo-mandibularis, digastricus, 
pterygoideus intemus, and mylo-hyoideus. Clean these muscles and 
study them. * 

Dissect the temporo-mandibular joint. Open the joint capsule and 
examine the articular disc. 

Remove the mandible and lay the preparation with its ventral surface 
upward. 

Examine the dorsal part of the guttural pouches and study the Eusta- 
chian tubes. Is the term ''tube" at all misleading? What muscles lie 
along the outer surface of the tubes? Note the median recess of the 
pharynx between the expanded anterior ends of the tubes. 



11 



Rcmo\'c the remnants of the <^uttural pouches, and clean and dissect 
the ventral muscles; these comprise the lon^us colli, and the recti capitis 
major, minor, lateralis. 

Remove the muscles from the articulations formed between the axis, 
atlas, and occipital bone, and dissect these joints. 

Disarticulate the atlas from the skull, cutting through the spinal cord 
and its membranes. Remove the dorsal arch of the atlas. Examine the 
... spinal cord and its membranes, and remove these to expose the odontoid 
ligament. 

Examine the hard palate, gums, teeth, and posterior nares. 

Examine the eyelids and conjunctiva. Separate the lids from the 

orbital margin. Find and examine the lacrimal gland and its ducts. 

Separate the gland from the supraorbital process. Saw through the root 

of the process and through both ends of the zygomatic arch, and remove 

the piece of bone thus isolated. This opens up the orbit for dissection. 

Remove any remaining orbital fat. 

433 The eyeball with its muscles, vessels, and nerves is enclosed in the 

439 periorbita. Examine this sheath, then slit it lengthwise and reflect the 

flaps. Clean the ocular muscles and separate them from each other. In 

doing this one dissector should fix the eyeball with a hook in the sclera in 

the various positions necessary to deal with the several muscles. The 

retractor is visible when the recti are cut across and reflected. The 

optic nerve is enclosed in the retractor. 

__Q Examine the eyeball. Remove the cornea and examine the iris, 

560 P'^pil' ^^^ l^^s. Section the eyeball through its equator and examine 

561 the interior of both pieces. 

The paranasal sinuses of one side are now to be opened up fully by 
removing their outer wall. With hammer and chisel make two openings 
above the facial crest, one above the anterior part of the crest, and the 
„g other just in front of the orbit. Remove with bone forceps the outer wall 
40 of the maxillary sinus, retaining the facial crest and the septum between 
the anterior and posterior compartments of the sinus. Explore the 
sinus thoroughly. 

Make an opening midway between the internal canthus and the median 

• line, and remove the outer wall of the frontal sinus. Explore the sinus fully. 

Make a sagittal section of the skull about a quarter of an inch from the 

median plane, i. c., toward the side on which the sinuses have been opened 

up ; be carefiil not to attempt to saw through the incisor tooth — finish here 

with a chisel. Wash the sections and study the nasal cavity. If the 

238 section is successful the septum nasi is seen on the larger piece, and the 

36 turbinal bones, lateral mass of the ethmoid, and meatuses can be examined 

on the other. 



12 



i 



On the smaller portion find the naso-maxillar}" fissure. Open up the 
posterior parts of the turbinal bones. Dissect the mucoas membrane off 
their cartilaginous prolongations. Note the course of the infraorbital 
canal and the naso-lacrimal canal and duct ; to see these completely remove 
the turbinal bones. Explore the spheno-palatine sinus. 

Make two cross-sections of the larger piece of the skull, one at the 
anterior end of the facial crest, and the other through the anterior part of 
the orbit. Be careful not to attempt to saw through the teeth; finish here 
with a chisel. Study the sections, noting especially the septum nasi, 
turbinal bones, and nasal meatuses. 

Remove the brain, noting the points of exit of the cranial nerves. 
Examine the exterior of the brain and identify its gross divisions. Detach 
the dura mater and examine the inner surface of the cranial wall; note 
the relations of the parts of the brain to the wall. 



347 



37 
348 



13 



466 



THE THORAX AND THORACIC LIMB. 



PECTORAL REGION. 

Find by palpation the cariniform cartilage of the sternum. From this 
a median furrow extends backward to a depression which indicates the 
position of the xiphoid cartilage. Palpate the ventral border of the 
sternum. On the front of the breast there is a central furrow between 
the anterior superficial pectoral muscles, and between these muscles and 
the mastoido-humeralis there is a lateral furrow on either side. Can you 
recognize the cephalic vein in this furrow? The limb should be abducted. 

Make a median incision of the skin from the cariniform cartilage to the 
xiphoid cartilage. This will be extended backward by the dissectors of 
abdomen. Make a transverse incision from the cariniform cartilage to 
the point of the shoulder, and another from the xiphoid cartilage outward; 
extend the latter about half way up the lateral wall of the thorax. Reflect 
the flap of skin and fasten it out of the way. 

The pectoral fascia is now to be examined and removed. Is it closely 
adherent to the muscles? 
177 Note the position of the large cephalic vein. Is it accompanied by 
186 an artery? 

Find the line between the anterior and posterior superficial pectoral 
muscles. The plane of division here is very oblique, since the anterior 
muscle overlaps the posterior one to a considerable extent. If in doubt, 
dissect under the anterior part of the anterior superficial pectoral and 
complete the separation. 

Raise the anterior superficial pectoral muscle and cut it across about a 
handbreath from its sternal attachment. Reflect the inner part to its 
sternal attachment. Reflect the outer part to the deltoid tuberosity, 
where it joins the mastoido-humeralis. 

The posterior superficial pectoral is now exposed. Dissect under its 
posterior part and cut it across about a handbreadth from the sternal 
attachment. In doing this it must be separated pari passu from the deep 
muscle to avoid damage to the latter. Reflect both pieces to their attach- 
ments. It is convenient for the dissectors on one side to reflect the medial 
flap while those on the other side reflect the lateral flap. 

Clean the deep face of the muscle-flaps and secure them out of the way. 
Clean the surface of the deep pectoral muscles as far as they are exposed. 
Find the line of division between the anterior and posterior muscles and 
separate them as far as is feasible at this stage. Note their direction and 
structure. Leave them intact for further examination and dissection in 
the natural position. 

14 



When the subject is suspended in imitation of the natural position 
replace the flaps of the superficial pectoral muscles and review them. 
Then re-examine the deep pectoral muscles. Abduct the limb and clean 
out the connective tissue between the shoulder and the chest wall. Here 
the brachial vessels and the brachial plexus of nerves are found. Clean 
and examine these. Separate the omo-hyoideus from the mastoido- 
humeralis. Note here the prescapular lymph glands which lie on the 
anterior border of the anterior deep pectoral muscle. 

Cut the mastoido-humeralis and the omo-hyoideus across in front of 
the shoulder. Reflect the former so as to expose the anterior deep pectoral; 
clean the surface of this muscle and study it. 

Cut the anterior deep pectoral muscle across a little below the shotdder, 
and separate the two parts from the posterior deep pectoral. Clean 
and examine the latter. 

Cut the posterior deep pectoral muscle across about a handbreadth 
from its origin. 

THE BACK. 

178 

The fasciae and the muscles which extend from the neck and trunk to 179 

the thoracic limb are to be dissected in collaboration with the dissectors 523 
of adjacent parts. The skin is to be removed from the back and loins. 

Examine the panniculus camosus and the superficial fascia. Then 
remove these, but leave for future examination the parts of the muscle 
which go to the inner surface of the arm and into the fold of the flank. 

Study the lumbo-dorsal fascia. This is to be kept intact till a later 
stage. 

Clean the surface of the trapezius thoracalis. Note the large dorsal 
branch of the spinal accessory ner\'e entering its deep face. Cut the 
trapezius across about a handbreath from its upper attachment, Reflect 
both flaps. 

Clean the surface of the latissimus dorsi. The insertion is not visible 
now and must be examined later. Cut the muscle across about a hand- 
breadth behind the shoulder. Reflect the upper part to the fusion of its 
aponeurosis with the lumbo-dorsal fascia. Be careful not to cut the latter 
nor to injure the thin aponeurosis of the serratus anticus. 

Clean and examine the funicular part of the ligamentum nuchae 
at the withers. Remove the loose connective tissue from the scapular 
cartilage and the rhomboideus muscle. 

Clean the serratus magnus as far as it is now exposed, including its 
interdigitations with the obliquus abdominis extemus. Abduct the limb 
strongly so as to see the part of the muscle naturally concealed by the 
shoulder and arm. Sever the attachment of the muscle to the scapula, 
cutting close to the bone. 



15 



Now adducl the linilj as much as possible to open up s])ace ])ctween the 
scapular cartilajj^e and the rhoTnl)oideus thoracalis. Examine this muscle 
and cut it across. In doin^ this be careful not to cut the underlying 
dorso-scai)ular ligament to which the muscle is attached. Scra]3e the 
muscle-flaps off the ligament. 

Remove the limb, lay it aside and resume the dissection of the thorax. 

Complete the removal of connective tissue from the surface of the 
serratus magnus. Note the large nerve running backward across the 
aponeurosis on the surface of the muscle, which it innervates. Examine 
the stump which was attached to the scapula; the bundles arc here inter- 
sected by numerous elastic lamellae given off from the dorso-scapular 
ligament. Note the relation of the posterior digitations with those of 
the external oblique muscle. 

Examine the thoracic attachments of the pectoral muscles and 
remove them. 

Clean and examine the rectus thoracis and the anterior parts of the 
rectus abdominis and obliquus abdominis externus 

With the dissectors of the head and neck, turn down the serratus 
magnus to its costal attachment and cut the muscle across a little above 
the latter. 

Study now the dorso-scapular ligament. Remove the rhomboideus 
from its surface. It will be seen that the so-called ligament is a special 
thickening in the withers of the lumbo-dorsal fascia. What muscles are 
attached to it? Reflect from below upward the superficial elastic lamina 
given off from the ligament, exposing the serratus anticus. Clean and 
examine this muscle. 

Cut the serratus anticus across just above its costal attachment and 
reflect both flaps. 

The transversalls costarum is exposed, and a thin lamina from the 
dorso-scapular ligament is seen coming down over the longissimus and 
dipping in between the two muscles to be attached to the ribs. Cut this 
lamina longitudinally and reflect the flaps, exposing the longissimus 
and spinalis. 

Open up the furrow between these two muscles at the withers, and 
disclose a thin lamina detached from the deep face of the dorso-scapular 
ligament. The aponeurosis of the complexus dips in here to be attached 
to the transverse processes of the thoracic vertebrae. Turn down the 
longissimus dorsi to see this attachment. 

Clean the surface of the transversalis costarum and separate its inner 
border from the longissimus. Note that a layer derived from the lumbo- 
dorsal fascia dips in between the two muscles here and is attached to the 
ribs. Expose the deep set of tendons of the transversalis and separate 
the bundles as far as any natural division exists. Remove the muscle, 
but leave stumps of its attachments to the ribs. 

16 



N 



i 



I 



Remove the longissimus and clean and examine the multifidus and 184 
the levatores costarum. 

Clean and examine the external intercostal muscle in one or two 
intercostal spaces. What is the direction of the fibres? Does it extend 
the entire length of the space? Remove the external intercostal muscle 
and expose the internal one. Note the direction of the fibres of the latter. 
Does it extend the entire length of the space? What is the direction of 
the fibres in the lower part of the spaces? Note the position of the inter- 
costal vessels and nerves. 

THE THORACIC CAVITY AND VISCERA. 

Open the thorax by removing the greater part of its lateral walls. It 
is advisable to leave in situ the first, third, sixth, and last two ribs. Saw, 
or cut through with heavy pincers, the other ribs near their vertebral 
ends. As far back as the tenth rib nick the costo-chondral junctions 
with the cartilage knife and turn the ribs downward; in this way any rib 
may be replaced in its natural position for topographic purposes. From 
the tenth backward the ribs are to be severed at a gradualh^ increasing 
height, just above the costal attachment of the diaphram. Take care 
not to injure the lungs. 

The lungs are now to be examined. If the subject has been preserved 
properly, the lungs will have approximately the size and shape which 263 
exists during life. When the thorax of an unpreserved subject is opened 
the atmospheric pressure causes immediate collapse of the lungs, and 
inflation of them gives only an imperfect idea of their true shape and size. 

Note that the costal and basal surfaces, the borders, and the apex have 
no attachment to the wall in normal cases. Determine how and where 
the lung is attached. Observe the cardiac notch on each side. 

It is advisable to remove the left lung first. Take hold of the base and 
draw it outward a little. Cut carefully through the ligament of the lung 
from behind forward. It is evident now that the two lungs are adherent to 
each other from the ligament forward to the root. Dissect them carefully 
apart, endeavoring to avoid injury to the mediastinal pleura. The root 
of the lung is now to be dealt with. Turn the apex of the lung back, and 
cut the pleura as it is reflected upon the root. The bronchus can no\v be 
felt. On this are the pulmonary nerves and the relatively small bronchial 
artery. Divide these structures from above downward. The left branch 
of the pulmonary artery is now reached, and is also to be cut across. 
Below and behind the artery are the pulmonary veins; in dividing these 
take care not to damage the heart. Find the bronchial l3nTiph glands. 

Now study the mediastinal surface of the lung and observe how its 
various features correspond with the surface of the mediastinum with 352 
which it was in contact. Identify the structures which compose the root 
of the lung. Note the line of reflection of the pleura; the surface of the 
lung enclosed by this line has no pleural covering. 

17 



.rtg P2xaminc the mediastinum and the or^^ans visible in it. Is the medias- 
tinum median? Does it fonn a eomplete septum between the two pleural 
eavities? Can you trace the mediastinal pleura in the dorso-ventral 
direction continuously at all points? Identify and study the form and 
position of the chief organs in the mediastinum. 
267 The right side of the thorax is to be opened like the left one, and the 
363 right lung dealt with in a similar manner. In removing this lung you will 
observe its mediastinal lobe, which lies on the other side of the posterior 
vena cava and the fold of pleura which extends down from that vessel; 
this fold must not be confused with the mediastinum. Compare the two 
lungs; in what important respects do they differ? Examine their structure 
and dissect the bronchi and larger pulmonary vessels in their ramification 
in the lung. 

Now explore the two pleural cavities. How do they differ? Note 
carefully the posterior limit of each, and mark this on the outside of the 
chest wall. Does the line of pleural reflection correspond exactly with the 
costal attachment of the diaphragm? Mark the latter on the chest wall. 
Endeavor to restore the natural curvature of the diaphragm, and note the 
relation of the costal part of the muscle to the chest wail.* How does 
this vary during respiration? 

358 Study cross sections of the thorax in order to understand the arrange- 

359 ment of the pleural sacs and the general relations of the thoracic organs. 

360 Ask for an explanation and demonstration of any features which are not 
clear to you. 

429 Note the position of the phrenic, vagus, cardiac, and sympathetic 
nerves. Identify the larger vessels, including the thoracic duct. 

Examine the course and relations of the oesophagus. The tube is 
usually tightly contracted. Remove portions of it and study its structure. 
How does the terminal part differ from that further forward? 

Expose the trachea and study its position and relations. Are the two 
bronchi alike in size and direction? 

Clean the outer surface of the pericardium. Study the form and rela- 
tions of the sac and the attachments of its fibrous layer. Open the peri- 
cardium by an incision on each side from base to apex and a horizontal 
incision carried around it at the level of the coronary groove. A variable 
amount of serous fluid — the liquor pericardii — escapes. When the flaps 
are reflected the serous layer of the pericardium is seen. Note the reflec- 
tion of this layer upon the great vessels at the base of the heart and its 
continuation on the surface of the heart to constitute the epicardium. 

With scissors cut away the pericardium along the line of reflection of 
its serous layer. Clean the great vessels above and below this line; and 
examine them. 



* Students should have at least once an opportunity of examining the thoracic 
surface of the diaphragm before the abdominal viscera are removed. 

18 



422 



Study the fonii, position and external features of the heart. When 270 
convenient compare its size in your subject with others. Remove the ^"^^ 
heart, together \\4th part of the great vessels. Clean and isolate the .^q 
aorta and pulmonary artery. How are these vessels connected? What 421 
is the transverse sinus of the pericardium? Note the arrangement of 
the auricles as viewed dorsally. Clean the epicardium and fat off the cor- 426 
onary vessels. Examine the latter and remove them with the exception 427 
of a short piece of their origin. 

Remove parts of the walls of the cavities by incisions parallel with the 
grooves of the heart; ask an instructor to demonstrate the procedure. 
Wash out the cavities and explore them with the aid of the description in 
in your text book. Sectional views are also very instructive. Follow .^a 
the course of the blood through the heart and lungs so as to associate the 
structures \vith their mechanical fimctions. 

Dissect away the atria and cut the aorta and pulmonary artery off 
short. The form and position of the four orifices of the bases of the 425 
ventricles are now well seen. Examine the aortic and pulmonary valves. 
A cross section of the ventricles shows the shape of these cavities and the 
thickness of their walls. 

Remove the pleura from the floor of the thorax and note the sternal 
attachment of the pericardium. Remove the latter except its apex. 

Clean the surface of the transversus thoracis and note its form 
and attachments. The internal thoracic artery and vein disappear under 
the anterior edge of the muscle. 

Clean the ventral part of the rim of the diaphram and note carefully 
the attachment to the xiphoid cartilage and the adjacent costal cartilages. 
Examine the tendinous centre and observe the arrangements of its fibres. 
What foramen is found in this part? Clean the fleshy part of the crura 
and examine the two openings here. 

Remove the transversus thoracis and examine the sternal ligament 
and the chondro-stemal joints. 

Remove the trachea and bronchi and investigate their gross structure. 

Remove the pleura and vessels from the roof of the thorax and note the 
attachments of the thoracic parts of the longus colli and psoas muscles. 
What is the lumbo-costal arch? 

Clean the inferior common vertebral ligament. Dissect up the liga- 
mentum nuchae at the withers. Is a supraspinous bursa present? What 
is its position and extent? 

Remove three or four vertebrae with the vertebral ends of the corres- 
ponding ribs by sawing a piece out of the middle of the back. On this 142 
examine the vertebral and costo-vertebral joints. Open up the vertebral 519 
canal by sawing off the arches of the vertebrae. Examine the spinal cord 
and its membranes and the spinal nerves. Remove these and study the 
conjugal and superior common ligaments. 

19 



THE SHOULDER AND ARM. 

Before i)roceedin^ with the muscles of the shoulder, identify the 
stumps of the muscles which connect the limb with the trunk. These 
comprise, on the external surface, the trapezius and the mastoido-humer- 
alis. The insertion of the latter cannot well be worked out at present. 
The stumps of the following are found on the internal surface: 1. Both 
parts of the rhomboideus are attached to the inner surface of the 
cartilage of the sca]3ula. 2. The serratus magnus is usually cut off close 
to the scapula, but its area of attachment is easily defined; does it extend 
upon the cartilage at all? Note here the elastic lamellae derived from the 
dorso-scapular ligament. 3. The latissimus dorsi is to be cleaned, and 
the panniculus carnosus separated from it, but its tendon of insertion can 
be better dealt with later. 4. The omo-hyoideus ends on the subscapular 
fascia above the shoulder joint. Define its tendon of insertion. 5. The 
anterior deep pectoral muscle lies along the front of the shoulder. Clean 
it and note its insertion. G. The anterior superficial pectoral muscle 
accompanies the mastoido-humeralis to the front of the arm. 7. The 
posterior superficial pectoral muscle extends down the inner face of the 
arm and elbow; its insertion will be seen later. 8. The posterior deep 
pectoral muscle crosses the upper part of the inner surface of the arm 
almost horizontally. Blending with its tendinous upper edge is the tendon 
of the abdominal part of the panniculus carnosus. The large external 
thoracic or ^'spur" vein also runs along this edge. Clean the surface of 
the muscle and determine its insertion; then cut it across a handbreadth 
behind the attachment. 

The connective tissue on the inner surface of the shoulder is now to be 
removed. In doing this note the large brachial artery and vein which 
cross the inner surface of the shoulder joint and turn down along the arm; 
also the branches of the brachial plexus of nerves. Then remove these. 
^37 The subscapularis muscle is exposed. Behind the subscapularis is the 
teres major. At the shoulder joint the two muscles are separated by an 
inter\'al into which the subscapular vessels and the axillary nerve dis- 
appear. Clean out this space and extend the separation of the two muscles 
upward as far as any natural division can be made. The axillary lymph 
glands lie on the teres major at the level of the shoulder joint; examine 
and remove them. 

Reflect the skin as far as the inner surface of the elbow. Clean the 
surface of the posterior superficial pectoral muscle. Dissect up this 
muscle as far as the elbow and reflect it. 

The deep internal brachial fascia is now seen extending from the 
biceps brachii in front to the tensor fasciae antibrachii behind. Identify 
the internal tuberosity and the internal epicondyle of the humerus. Be- 
neath the fascia are the brachial artery and vein, accompanied by large 



20 



441 



nerves. Incise the fascia over the vessles and reflect it. On the vessels at 441 
the lower third of the arm are the cubital lymph glands. The vessels, 
nerves, glands, and connective tissue are to be removed. 

Clean the surface of the tensor fasciae antibrachii from below upward, ^g,^ 
Be careful not to injure the thin aponeurosis of origin which blends with 
the latissimus; leave them connected. 

Clean the common tendon of insertion of the teres major and latissi- 
mus dorsi; its attachment is concealed by the coraco-brachialis. Raise 
the stump of the latissimus dorsi and dissect it off the part of the aponeur- 
osis of the tensor fasciae antibrachii which arises from the posterior border 
of the scapula. 

Separate the tensor fasciae antibrachii from the long head of the triceps, 
beginning at the posterior border. The aponeuroses of the two blend at 
their scapular origin. Cut the tensor across a handbreadth above the 
elbow to facilitate the separation and reflect the flaps. 

The long head of the triceps is now largely exposed. In front of it is 
the relatively small internal head, Clean these and separate them. 

Clean the surface of the coraco-brachialis. Examine the long tendon 
of origin and its synovial sheath. The insertion is partly concealed by 
the biceps at present. 

Turn the limb over and begin the dissection of the external surface of 
the shoulder and arm. 

Reflect the skin as far as the elbow. The superficial fascia and the 
scapulo-humeral part of the panniculus carnosus are exposed. What is 
the direction of the fibres of the latter? Reflect the fascia and pannictdus 
as far as the elbow. 

Clean thoroughly the part of the mastoido-humeralis which covers the 
front and outer surface of the shoulder joint. Note that the upper part 
of the muscle is inserted into the deep fascia of the arm. 

Remove the superficial fascia from the muscles of the shoulder and from 
the triceps, but do not remove the glistening aponeurosis which covers a ^"^^ 
large part of the former. 

Reflect the stump of the mastoido-humeralis; its tendon of insertion 
dips in between the biceps and brachialis and will be followed later. 

Clean the lower part of the deltoid, but do not disturb its covering 
aponeurosis. A furrow indicates the posterior border of the muscle; 
dissect along this furrow from below upward, separating the deltoid from 
the triceps as far as the division is natural. Dissect up the anterior border 
from below upward till the aponeurosis is reached. 

Clean the lower part of the infraspinatus and supraspinatus. Between 
the long tendon of the infraspinatus and the deltoid there is a small triang- 
ular space in which part of the teres minor is visible. 

Cut the deltoid across a handbreadth above the deltoid tuberosity. 
Reflect the distal stump to its insertion. Dissect up the proximal part 

21 



178 



carefully off the lon<^ head of the triceps and the distal and posterior part 
of the infraspinatus as far as the fleshy part extends. It is now evident 
that the bulk of the muscle arises from the covering aponeurosis of the 
infraspinatus. 

The fleshy part of the teres minor is now partly exposed, but its tendon 
of origin is covered by the infraspinatus. Dissect up the posterior border 
of the teres minor. A sheet of fibrous tissue extends over the tendon of the 
infraspinatus and is attached to the superficial tendon of the teres minor; 
remove it and define the insertion of the teres. Raise the posterior border 
of the infraspinatus and dissect it carefully off the teres, from the tendon 
of which many fibres of the infraspinatus arises. 

Separate the distal third of the infraspinatus from the supraspinatus, 
working from below upward. Undermine the distal part of the belly of 
the infraspinatus and cut it across a couple of inches above the tendon. 
The proximal part may be easily reflected, taking the periosteum with it. 
Raise the distal stump and dissect its two attachments, taking care not to 
injure the capsule of the shoulder joint. The deep part is inserted into 
the upper edge of the posterior part of the external tuberosity of the 
humerus. Cut this attachment and reflect the long tendon. Note its 
structure and the bursa beneath it. 

Cut the teres minor across a couple of inches above its insertion and 
reflect both parts; do not injure the joint-capsule. Clean thoroughly 
the outer surface of the triceps. A furrow shows the line of separation of 
the long and external heads. Dissect them carefully apart, beginning in 
front. Is the separation at the insertion distinct? Raise the lower border 
of the external head and cut the muscle across a little in front of its middle. 
Dissect up both parts. In the case of the proximal stump there is no 
difficulty, but the separation of the lower part from the underlying anco- 
neus requires care. Begin at the lower border. 

Note the thick fascia which extends from the deltoid tuberosity to the 
external surface of the elbow joint. It bridges over the musculo-spiral 
groove and the brachialis muscle. What muscle arises in part from 
this fascia? 

The origin of the brachialis is now exposed. Find the small capsularis 
muscle. At the distal part of the arm you can recognize the external 
condyloid crest and the extensor carpi radialis arising from it. 

Replace all parts and review the region. 

Place the limb with its anterior surface facing you. Remove the 
anterior deep pectoral muscle with the exception of a short stump of its 
upper end. The supraspinatus is now exposed; clean its surface and 
define its borders. 

Clean the terminal part of the posterior deep pectoral muscle. The 
insertion is threefold. Some fibres are attached to the tendon of origin 
of the coraco-brachialis. The bulk of the fibres end on the anterior part 

22 



r 



of the internal tuberosity of the hmnerus, but a layer extends further 
forward and is attached to a tendinous sheet which stretches across from 
the inner to the outer tuberosity of the humerus. This sheet is a part of 
the fascial sheath of the biceps; it binds down the tendon of origin of the 
biceps in the bicipital groove, converting the latter into a canal. 

The biceps lies on the front of the arm, enclosed in a double sheath of 
fascia ; the latter is attached to the anterior parts of the tuberosities of the 187 
humerus and to the deltoid tuberosity, and is continuous below with the ^®^ 
deep fascia of the forearm. Slit this sheath lengthwise over the middle of 
the biceps and reflect it. Be careful not to damage the long tendon which 
extends from the biceps to the extensor carpi radialis and is not distinct 
from the deep fascia; it can be felt and should be artificially defined and 
retained. The tendon of the biceps is seen to occupy the bicipital groove, 
and the large bicipital bursa lies under the tendon here. Note that 
the bursa extends in part around the edges of the tendon to the superficial 
face of the latter. The origin of the biceps is concealed at present by the 
supraspinatus. Slit the lower part of the supraspinatus upward to expose 
the bicipital tuberosity (tuber scapulae) and the origin of the biceps. 
Are all of the fibres of the supraspinatus inserted into the lips of the bicip- 
ital groove? Note the large suprascapular nerve which passes outward 
between the supraspinatus and subscapularis. Cut the supraspinatus 
across at this point and follow both divisions to their insertions. The 
origin of the coraco-brachialis is exposed. 

Cut the biceps across at the middle of the arm. Reflect the proximal 
part and explore the bicipital bursa (bursa intertubercularis) . Note also 
the form and structure of the tendon of origin . Raise the distal stump 
and clean the insertion of the coraco-brachialis. 

The tendon of insertion of the mastoido-humeralis and anterior super- 
ficial pectoral muscles is now accessible. Take hold of the muscle stumps 
and tense the tendon and clean its surfaces. Note the radial nerve lying 
along its outer side and the anterior radial vessels at its inner side. Clean 
the front of the humerus. Replace the various parts and review the region. 

Complete the dissection of the inner surface. Cut the subscapularis 
across a handbreadth above the shoulder joint, and reflect both parts. 
The distal part is intimately attached to the capsule of the shoulder joint 
and is to be carefully separated from it. The capsularis muscle lies on the 
posterior surface of the joint capsule. 

Cut the teres major and latissimas dorsi across a handbreadth from 
the insertion and reflect both parts, taking the tensor fasciae antibrachii 
with the proximal part. This uncovers the origin of the long and inner 
beads of the triceps and the brachialis. The insertion of the latter may 
be exposed by cleaning the internal lateral ligament of the elbow joint 
and removing the fascia in front of it. Note that the inner fibres of the 
tendon of the biceps are attached to the ligament. 

23 



If desired, the lonf]j head of the triceps may be cut across about an inch 
from its origin, so that the shoulder joint may be examined on all sides. 
Review the arrangement of the muscles and tendons in relation to the 
shoulder joint. The only uncut muscles extending from the scapula to 
the humerus are the coraco-brachialis and capsularis. Cut the former 
below the joint. If there is no opening in the capsule the head of the 
humerus will remain in contact with the glenoid cavity when the limb is 
held up by the scapula. If the capsule is perforated the head of the 
himierus promptly drops about an inch. Disarticulate by a circular 
incision of the joint capsule. Examine the latter and the joint surfaces. 

Review the insertions of the muscles on the humerus. For convenience 
shorten the stump of the long head of the triceps. Follow the peculiar 
spiral course of the brachialis. 

THE FOREARM. 

Identify the bony prominences at each end of the region. Palpate the 
inner subcutaneous surface of the radius, which intervenes between the 
jyg extensor muscles on the dorso-lateral surface and the flexors behind. 
187 Note the form and position of the mass of horn known as the "chestnut. " 
190 Study figures of superficial dissections and see how much you can recog- 
nize on your specimen of what is shown there. 

Incise the skin down the middle of the anterior surface of the forearm 
and reflect it. 

The large cephalic vein extends from the distal end of the biceps to the 
**2 inner surface of the carpus. In front of it is the smaller accessory cephalic 
vein. 

Clean the aponeuroses of the posterior superficial pectoral and tensor 
fasciae antibrachii and follow them till they fuse with the deep fascia of 
the forearm. The first -named muscle may be removed. 

Remove the superficial fascia, exposing the deep fascia, and study 
the latter. 

Place the limb with its anterior surface facing you, and identify the 
190 extensor muscles. The fascial compartments in which the muscles lie 
are to be opened up by slitting the fascia lengthwise over the middle of each 
muscle, NOT along the furrows between the muscles. Incise the fascia 
over the extensor carpi radialis, i. e., practically down the middle of the 
anterior surface of the forearm. In doing so be careful not to cut the 
tendon of the extensor carpi obliquus, which crosses the extensor carpi 
radialis in the distal third of the region ; also preserve the long tendon of the 
biceps. Reflect the fascia on each side of the incision, beginning below. 
At the upper part of the region fibres of the muscle arise from the fascia 
and must be cut off it. The inner flap is attached to the inner border of 
radius. The outer flap dips in between the extensor carpi and anterior 



24 



i 



# 



i 



extensor as an intermuscular septum. Open up the fascia in a similar 
fashion over the anterior and lateral extensors of the digit and the extensor 
carpi obliquus. It is best not to dissect as far down as the synovial 
sheaths of the extensor tendons at present. But in case you have done so, 
insert a probe into the sheath and determine its extent upward and down- 
ward. Mark the upper limit on the tendon by nicking the latter slightly. 

Clean the fleshy part of the extensor carpi obliquus. 

Dissect the outer side of the extensor carpi radialis from the inter- 
muscular septum, working from below upward. 

Clean the anterior extensor. Find the small tendon of the radial 
head which lies along the outer border of the chief tendon. Dissect 
upward along this and isolate the radial head so far as a natural separation 443 
exists. Can you find the very small ulnar head in the middle of the 
region? It comes from the ulna at the level of the interosseous space, 
but its upper part is concealed by the radial head and the lateral extensor 
at present. 

Place the limb with its posterior surface facing you. Slit the fascia 
from the accessory carpal bone to the olecranon, and also divide it trans- 
versely a little below the fleshy part of the tensor fasciae antibrachii. 
Reflect the inner flap to its attachment to the radius. Reflect the outer 
flap similarly. Are any intermuscular septa given off? 

The ulnar head of the deep flexor of the digit forms the posterior 
contour of the forearm in its upper fourth. Below this there is a furrow 
between the external and middle flexors of the carpus, in which the ulnar 
vessels and nerve lie. Remove the vessels and nerve and open up the 
furrow; find here the slender tendon of the ulnar head of the deep flexor 
and follow it upward to the belly of the muscle. Separate the latter from 
the flexor carpi extemus. 

Lay the limb on its outer face. Clean the flexor carpi intemus, which 

lies behind the subcutaneous surface of the radius. Note the posterior ^^ 

187 
radial vessels and median nerve disappearing under the upper part of the 

anterior border of the muscle. Cut these off at this point and clean the 

internal lateral ligament of the elbow joint if this has not been done. Is 

there any trace here of a pronator teres muscle? If so, call the attention 

of an instructor to it. 

Dissect along the anterior border of the flexor carpi medius from below 
upward. Take care in dissecting up the posterior border not to cut the 
thin ulnar head in the proximal third of the forearm. The ulnar vessels 
and nerve lie beneath this head, and may be removed. Clean the inner 
surface of the ulnar head of the deep flexor. 

Lay the limb on its inner surface, and clean the flexor carpi extemus, .g. 
The deeper dissection of the region should be deferred till the lower part 
of the limb (the manus) is dealt with. 



25 



CARPUS, METACARPUS, AND DIGIT. 

^^^ Identify the bony prominences of the lower part of the limb. Study 
fibres of superficial dissections and endeavor to recognize the ligaments 
522 and tendons shown in them. 

Incise the skin down the middle of the anterior surface of the limb and 
reflect it, cutting it from the upper border of the hoof as far as necessary 
at this stage. 

Examine the superficial fascia and reflect it in a similar manner. 
The deep fascia is strengthened by transverse fibres at the distal end 
of the forearm and at the carpus, forming the anterior annular ligament of 
the carpus. The extensor tendons and their synovial sheaths here must 
be carefully examined. Study figures illustrating these, and if you do 
not understand the arrangement, ask an instructor for a demonstradon. 
Try to inflate the synovial sheaths with the blowpipe or insert a probe 
and determine their extent upward and downward. Slit them open and 
note the character of the inner surface and the glistening appearance of 
the tendon covered with synovial membrane. Find the mesotendon. 

Note the marked increase in size of the lateral extensor tendon below 
the carpus. How is it accounted for? 

Clean the tendons below the carpus and also the metacarpal bones and 
first phalanx in so far as they are free. Clean and define the anterior 
annular ligament of the fetlock and the branches of the suspensory liga- 
ment which join the extensor tendon on the front of the digit. Find the 
bursa under the anterior extensor tendon at the fetlock joint. 

Remove the rest of the skin from the limb and turn the posterior face 

of the latter toward you. Remove the superficial fascia. In doing so 

447 note the metacarpal and digital vessels and nerves on either side of the 

522 flexor tendons. Look for the small band which descends on either side of 

the digit from the fibrous basis of the ergot ; also the delicate tendons of the 

internal and external interossei above the fetlock. 

The dissection of the deep fascia requires much care and patience. 
Note its great thickness from the distal part of the forearm to about the 
middle of the metacarpus. It is attached to the accessory carpal bone, 
the internal lateral ligament of the carpus, and the small metacarpal 
bones. Above the carpus it blends with the tendons of the middle and 
194 external flexors of the carpus. At the carpus it forms the posterior annular 
^^ or transverse ligament of the carpus, which completes the carpal canal. 
This ligament is extremely thick, and is partially divisible into two or 
three layers, between which lie large veins, an artery, and a nerve, and at 
the inner side, the tendon of the flexor carpi intemus. 

Define and follow to their insertions the tendons of the flexors of the 
carpus. Clean the lateral ligaments of the carpus. 



26 



f 



I 



442 



Open up the carpal canal by slitting the transverse ligament vertically. 
What are the attachments of the ligament? What does the canal contain? 
Explore the carpal synovial sheath and mark its upper and lower limits 
by nicking the flexor tendons. 

The flexors of the digit are now to be dissected. Cut the flexor carpi 
intern us across at the middle of the forearm, and dissect up both parts. 
The median nerve, the posterior radial artery, and usually two satellite 
veins are now seen descending on the muscular mass behind the radius. 
Examine and remove them, together with the connective tissue about 
them. Cut the flexor carpi medius at the middle of the forearm, and 
dissect up both parts. 

The flexors of the digit are now exposed, and are to be separated from ^93 
below upward to avoid error. Begin below the carpus and dissect up the 
superflcial flexor tendon. Take care not to cut the radial or superior 
check ligament when dissecting along the inner side at the lower third of 
the forearm. Do any of the fibres of the ligament go to the deep flexor? 
The belly of the superficial flexor is closely adherent to the deep flexor, 
and must be carefully isolated. 

The superficial flexor may be cut across at the middle of the forearm if 
found desirable in order to facilitate dissection of the deep flexor. In 
dealing with the latter begin at the carpus, and use the three tendons as 
means of isolating the three heads. It is not neccesary to subdivide 
the htmieral head. 

It is advisable at this stage to remove the hoof. In well-preserved 
subjects the hoof usually adheres very closely and its matrix is therefore 
damaged more or less extensively in the process of removal.* With a car- 
tilage knife separate the upper part of the wall of the hoof from its 
matrix. Saw through the wall from top to bottom at four places at 
least. Grasp the portions of the wall thus separated with hoof pincers 
and tear them off. If two saw cuts have been made near the heels it 
is usually possible to remove the part behind them together with the 
sole, frog, and bars. 

Dissect out the plantar cushion, which occupies most of the space 
between the lateral cartilages. Clean the cartilages and the wall and sole 
surfaces of the third phalanx. Note the insertion of the anterior extensor 
of the digit. 

Clean and define the posterior annular ligament of the fetlock and the 
two digital annular ligaments. Examine and remove the vessels and 522 
nerves which descend on either side of the flexor tendons and clean the 189 
tendons and the suspensory ligament in so far as they are exposed. In 
doing so look for the small lumbricales muscles. 447 

* The interior of the hoof and the matrix should be studied on iinpreserved mate- 
rial, from which the hoof can be removed in toto by immersing the digit in boiling 
water for ten or fifteen minutes or by allowing the hoof to be loosened by decompo- 
sition. 

27 



Separate the flexor tendons from above downward. Study illustra- 
tions of the digital synovial sheath (injected) and aceount for the pouches 
shown. Endeavor to inflate the sheath. Slit the posterior annular 
160 ligament of the fetlock vertically. Examine the ring formed here by the 
superficial flexor tendon. Explore the upper part of the digital sheath 
and mark its highest point on the tendons. 

Slit the digital annular ligaments vertically and reflect the flaps. 
What are their attachments? 

Cut through the ring of the superficial flexor tendon on one side and 
raise the tendon. Note the terminal bifurcation of the tendon and the 
insertion of the branches. Cut one branch and reflect the tendon. To 
expose the deep flexor more fully the superficial flexor may be removed 
after cutting its radial check ligament and other branch of insertion. 

Raise the deep flexor tendon at the upper end of the metacarpus and 
pass a finger downward into the lower part of the carpal sheath in front 
193 of the tendon. The subcarpal check ligament is in front of your finger. 
Clean the ligament and dissect it up as far as possible from the suspensory 
ligament. Cut the deep flexor tendon across just below the middle of 
the metacarpus. Dissect up the proximal part, taking the check ligament 
with it, as far as the upper end of the metacarpus. Turn down the lower 
part of the tendon. In doing so determine the lower limit of the digital 
sheath and mark it on the tendon. Just below it a layer of connective 
tissue extends from the tendon to the capsule of the coffin joint; cut through 
151 this layer, keeping close to the tendon. The navicular bursa is opened; 
expose it, noting carefully its position and extent. 

What three pulleys does the deep flexor tendon pass over? Examine 
the deep face of the tendon, observing its form and structure at different 
points. Note its insertion. 

THE ELBOW JOINT. 

Review the arrangement of the muscles about the elbow joint. 

Cut the tendon of the biceps which joins the extensor carpi radialis. 
Pull the lower stump of the biceps inward and cut the deep principal 
insertion to the bicipital tuberosity of the radius. Sever the superficial 
insertion from the internal lateral ligament. Cut the brachialis across 
at the middle of the arm, and reflect the lower part to its insertion under 
the long internal lateral ligament; it may be cut off short here. Cut the 
extensor carpi radialis and anterior extensor of the digit across a hand- 
breadth below the elbow and dissect up the proximal stimips to their 
origin; cut them off, leaving short stimips. The front of the elbow joint 
is now exposed, and the joint capsule is to be cleaned. 

Remove the anconeus carefully from, the posterior part of the joint 
capsule. It is hardly possible to remove the flexors of the carpus and 
digit without opening the pouches of the synovial membrane of the joint 
which extend down a short distance under them. 

28 



144 

to 



Open up the joint capsule both in front and behind, and explore the 
joint cavity. 

Note the attachments of the lateral ligaments and define them clearly. 
Cut the long part of the internal ligament across over the insertion of the 
brachialis to expose the latter. Disarticulate the joint and examine the 
joint surfaces and the attachment of the joint capsule. 

Expose the interosseus space and examine the tranverse or arciform 
ligaments. 

The lower part of the limb may be separated by sawing through the 
lower third of the forearm and cutting any soft tissues. 

THE CARPAL JOINTS. 

Clean the anterior part of the carpal joint capsule. It blends on either 
side with the lateral ligaments. The latter give attachment to the carpal 
fascia and hence they have a rather rough surface when the fascia is re- 147 
moved. The lateral extensor tendon descends in a canal in the external 
lateral ligament. 

Note the bands which extend from the accessory carpal to the meta- 
carpus ; they transmit the pull of the external and middle flexors of the 
carpus. 

The posterior part of the capsule (posterior ligament) is very thick 
and is closely adherent to the underlying bones. It forms the smooth 
anterior wall of the carpal canal. How is it continued downward? 

Remove the anterior part of the capsule and note the three synovial 
sacs. Flex the joint and observe the movements of the bones. Clean 
the small ligaments. 

Take hold of the check ligament and forcibly remove the posterior 
part of the joint capsule. Examine the small ligaments here and the upper 
attachment of the suspensory ligament. 

Disarticulate the radio-carpal and intercarpal joints, but leave the 
distal row connected with the metacarpus 

THE SESAMOIDEAN LIGAMENTS. 

The superior sesamoidean or suspensory ligament of the fetlock has 150 
been exposed in the previous dissection. Clean and examine the ligament ^^^ 
carefully, noting its form, position, and attachments. .g. 

Examine the intersesamoidean ligament and the smooth pulley formed 193 
by it and the sesamoid bones at the fetlock. 

Dissect carefully the inferior sesamoidean ligaments. Observe that 
all of these ligaments form a continuous stay apparatus, in which the 
sesamoid bones are intercalated at the point of greatest pressure; note 
further the branches of the suspensory ligament which go forward to the 
extensor tendon. It is interesting to cut the suspensory ligament above 
the fetlock, noting the effect on the digital joints when weight is put 
on the limb. 



THE FETLOCK JOINT. 

Dissect Up the extensor tendons, noting their attachments and bursa 
here. Clean the anterior part of the capsule and the lateral ligaments. 
Endeavor to inflate the capsule and note especially how it pouches upward 
behind the lower part of the large metacarpal bone. Open the front of the 
joint and explore the cavity here. Cut the lateral ligaments, remove 

148 the metacarpal bone, and examine the joint surfaces. Find the short 

149 sesamoidean ligaments. 

THE PASTERN JOINT. ' 

The anterior surface of the joint is covered by the wide extensor tendon, 
and the synovial membrane is attached to the deep face of the tendon. 

161 Clean the lateral ligaments. What structures lie on the posterior surface 
of the joint? Dissect the volar ligaments. Reflect the extensor tendon 
and examine the joint surfaces. 

THE COEEIN JOINT. 

The front of the joint is covered by the broad terminal part of the 
IQl extensor tendon, to the deep face of which the synovial membrane is 

162 attached. 

Remove part of the lateral cartilage to expose the side of the joint. 
Observe how the joint capsule pouches out against the deep face of the 
cartilage. Clean the lateral ligaments. 

Remove the deep flexor tendon. Clean the suspensory ligaments of 
the navicular bone. Note the pouch of the joint capsule above the level 
of the navicular bone. How is the joint capsule reinforced below the 
navicular bone? Remove the second phalanx and examine the joint 
surfaces. 



30 



THE ABDOMEN, PELVIS, AND PELVIC LIMB. 



i 



THE ABDOMINAL MUSCLES AND TUNIC. 

Find the median depression which indicates the position of the xiphoid 
cartilage. From this follow the costal arch and locate the last rib. Note 
the median raphe of the skin and examine the umbilicus. If the subject 
is a gelding look for scars or depressions resulting from the castration 
incisions. Are the stumps of the spermatic cords adherent to the skin? 
Palpate the external inguinal ring and the prepubic tendon. Study the 
external part of the prepuce and its cavity. If the subject is a stallion 
examine the scrotum, if a mare study the mammary glands. Note the 
arrangement of the fold of the flank on either side. Can you trace the 
large external thoracic vein? 

Make an incision of the skin just to one side of the ventral median line 
from the xiphoid cartilage to the prepubic tendon, but leave a ring of skin 
around the preputial orifice. From this carry an incision transversely in 
a plane behind the last rib. Another transverse incision is to be made 
from the xiphoid cartilage outward and upward to a horizontal line on a 
level with the point of the shoulder. Reflect the large anterior flap as far as 
the origin of the external oblique muscle (refer to text figure for this). 
Reflect the small posterior flap and secure it to the inner surface of the 
thigh. Take care to reflect only the skin. Is this difficult? Why? 

Examine the superficial fascia and the abdominal part of the panniculus 
camosus; clean the latter and observe the external thoracic (spur) vein. 
Cut these across along lines corresponding to the skin incisions and reflect 
them. 

Slit the prepuce along the ventral median line and expose the fascia 
penis and penis. Examine these and reflect the penis far enough to expose 
the prepubic tendon. Note the large venous plexus about the penis. 

If the subject is a mare, the mammary glands are to be examined 
and removed. 

The abdominal tunic is now exposed, and after examination is to be 
removed in great part. This procedure is somewhat tedious. Begin 
laterally over the fleshy part of the obliquus abdominis extemus. Remove 
the tunic in strips in the same direction as the fibres of the muscle. Much 
care is necessary when dissecting the tunic off the external oblique to 
avoid injury to the latter. It is best to leave the tunic on ventrally where 
it is partly interwoven with the aponeurosis, but it must be carefully 
removed in the inguinal region, so that the external inguinal ring is prop- 
erly exposed. Remove the tunic from the digit ations of, the serratus 
magnus which dovetail with those of the external oblique. 

31 



178 
186 



178 
186 



The major part of the obHquus abdominis externus is now exposed. 
Note its line of origin. Have the fibres all the same direction? Cut the 
muscle across about a handbreadth from its origin, and also incise it 
transversely in the flank a short distance behind the last rib. This latter 
incision is to be carried from the upper part of the flank to the outer edge 
of the rectus abdominis, i. e., to the place where the aponeurosis of the two 
obHqui blend. Reflect the upper part of the muscle to its origin. Begin- 
ning in front of the flank incision reflect the lower part and the aponeurosis 
till the latter blends with that of the internal oblique. Behind the flank 
incision it is necessary to cut the aponeurosis of the external oblique 
alongside of the linea alba to permit of reflection of the posterior part. 
Care is necessary here as the aponeurosis is thin and easily torn. 

The obliquus abdominis intemus is now largely uncovered and is to 
j^yg be cleaned. Its fleshy part is to be cut across in a direction corresponding 
to the flank incision of the external oblique. Reflect the anterior part to 
its attachment to the costal cartilages and the line of fusion with the apon- 
eurosis of the external oblique. Cut the posterior part of the aponeurosis 
along the linea alba, and dissect the aponeurosis and the corresponding 
fleshy part off the underlying rectus and tran versus abdominis. 

Continue the exposure of the rectus abdominis by dissecting off it 
the aponeurosis of the oblique muscles, together with the abdominal 
tunic, in so far as the latter has been retained. To do this the layer formed 
by the three structures mentioned must be cut alongside of the linea alba 
and separated carefully from the inscriptiones tendineae of the rectus. 
Do not cut awa}^ the posterior attachment of the posterior deep pectoral 
muscle in the effort to expose the anterior part of the rectus ; this part will 
be uncovered later after the dissection of the pectoral muscles. 

After examination of the rectus abdominis, cut the muscle across in 
the same line as in the case of the obliqui. Reflect the flaps, cutting also 
alongside of the linea alba. 

The trans versus abdominis is now largely exposed. Clean the fleshy 
part and dissect along the inner side of the costal arch till the attachment 
there is visible. The deep surface is related to the transversalis fascia 
and the peritoneum. In horses in good condition there is a considerable 
layer of fat between the transversus and the peritoneum, but in the ema- 
ciated subjects generally use.d for dissection this is almost entirely absent. 

When ready for the removal of the viscera, cut the transversus in a 
transverse direction as done with the other muscles, and also incise it 
alongside of the linea alba. 

THE ABDOMINAL VISCERA. 

The animal is to be secured squarely on its back. If the subject has 
been used for the dissection of the muscles the abdomen has been opened. 
If not, two incisions are to be made through the ventral and lateral walls 

32 



of the abdomen. A median incision is carried from the xiphoid cartilage 
to the prepubic tendon, and a transverse incision is made a Httle behind 
the last rib; the latter may extend to the outer edge of the longissimus. 
In opening the abdomen care must be taken not to cut into the large 
intestine, especially if the bowel is distended. Make carefully a small 
incision down to the peritoneum and perforate the serous membrane with 
the finger. From this opening the incision is to be extended in both 
directions. In this procedure pass the fingers between the abdominal 
wall and the bowel, the palm of the hand being toward the wall, and with 
the other hand introduce the scalpel with its back against the hand in the 
abdomen. The fingers of the hand in the cavity are kept a little in advance 
of the point of the knife and thus prevent the bowel being cut. It is much 
more convenient to use a probe-pointed bistoury for this purpose. Reflect 
the flaps and secure them out of the way. 

Examine and identify the parts of the intestine now visible, but do 
not disturb them unnecessarily. Determine next the relationship of the 269 
intestine to the lateral walls, inclining the subject first to one side, 
then to the other, for this purpose. 

Take hold of the left part of the great colon and draw it backward a 
little so as to see the two anterior flexures, the ventral or sternal and the 
dorsal or diaphragmatic. 

Draw the apex and body of the caecum toward the right flank. Note 
here the caeco-colic fold. Find the pelvic flexure of the colon and note its 
form and position before it is displaced. 

Raise the left parts of the great colon and lay them on the breast, 
straightening out the anterior flexures as nearly as practicable. Examine 
the right parts of the great colon. 

Coils of the small intestine and small colon are now exposed and the 
stomach (covered by the great omentum) is partly visible. Part of the 
liver and of the spleen can be seen. Study the arrangement of the small 
intestine ; spread enough of it out to examine the great mesentery. Draw 
the coils of small intestine over the left flank, disturbing the small colon as 
Httle as possible in doing this. Find the beginning of the mesenteric 
portion of the small intestine; it lies ventral to the left kidney and just 
behind the origin of the small colon. Note here the end of the mesoduo- 
denum, which attaches the duodenum closely to the origin of the small 
colon. Apply two ligatures to the beginning of the mesenteric part, 
about a handbreadth apart, and divide the bowel midway between them. 
Find the terminal part of the small intestine (ileum) and its junction with 
the caecum. Is the small intestine here at the edge of the mesentery? 
Apply two ligatures a handbreadth apart and about a foot from the 
ileo-caecal junction and divide the bowel between them. Now pass one 
hand under the root of the mesentery, gather up the latter, and cut it 
across. Lay the small intestine aside for further examination. 

33 



Examine the small colon. How does it differ from the small intestine? 
After noting its position, draw it out of the cavity and spread it out so as 
to display the colic mesentery. How does the latter differ from the great 
mesentery? Note carefully the position of the junction of the small colon 
with the large, as this is constant. What is the shape of the bowel here? 
Are there any coils of the small colon in the pelvic cavity? Examine 
other subjects in regard to this. Find the junction of the small colon 
and rectum. Divide the bowel here, first applying ligatures if deemed 
necessary. Cut the colic mesentery a short distance from the sublumbar 
attachment, and draw the small colon — except its origin — out of the 
abdomen. 

Incline the subject toward its left side, and carry the caecimi and large 
colon as far as possible in the same direction. This exposes the- pyloric 
part of the stomach and the greater part of the duodenum, as well as the 
right lobe of the liver. 

This is the most favorable point for the study of the great omentum. 
Read a description of it. Spread the omentum out and make an opening 
into its cavity, which is evidently only a potential one in its undisturbed 
state. Note especially at this stage its colic attachment, as this must be 
severed to remove the bowel. Find the epiploic foramen (of Winslow). 
Examine the duodenum and mesoduodenum. 

The next step is the separation of the caecimi and colon from the roof 
of the cavity. Care and skill are required in this procedure to avoid 
opening the bowel — an accident which is decidedy disagreeable and 
should not occur.* If the intestine is much distended it is well to allow 
most of the gas to escape through a valvular opening made in the wall of part 
of the bowel which is outside of the abdomen. Cut the attachment of the 
great omentum and mesoduodenum to the colon and caecum. Press 
down with the outstretched fingers the right dorsal part of the colon, and 
carefully cut through the peritoneum which passes from it to the abdom- 
inal wall. Then with the fingers push back the connective tissue till the 
right border of the pancreas appears. The gland is to be left in situ, so 
the bowel must be separated from its ventral surface. Use great care 
now, as the wall of the colon — devoid here of the peritoneal coat — is very 
easily perforated. The separation may be facilitated by gentle traction 
on the colon. In a similar way the base of the caecum is to be detached 
from the sublumbar region. Cut the caecal and colic vessels and remove 
the bowel. 

Study the structure of the small intestine. Examine the serous and 
muscular coats. Wash out and slit open several feet of the bowel, and 
examine the mucous membrane. Can you determine the presence of 
265 villi? Are Peyer's patches or solitary glands visible? 

* It is the practice of the author to have an instructor demonstrate this step 
before requiring students to do it. 

34 



I 



Next examine the caecum and colon. Note especially the arrangement 
of the bands. How is the body of the caecum attached to the colon? 
Separate these and find the junction of the ileum and colon with the caecum. 
Separate the base of the caecum from the great colon. Examine the great 
colon. Compare the diameter at different points. How are the dorsal and 
ventral parts attached to each other? Examine the mucous membrane. 
Open the caecum at its base and apex, and wash out its contents. Examine 
the ileo-caecal and caeco-colic orifices. Note the color of the mucous 
membrane and the extensive folds which project into the cavity of the 
bowel. Can you find solitary glands? 

Examine the small colon. Dissect away part of the mesentery to see 
the muscular band not now visible. Open up the bowel and note the marked 
constrictions of its lumen and the character of the mucous membrane. 

Return now to the cadaver and proceed with the examination of the 
viscera which remain in situ. Clean the ventral surface of the pancreas 273 
and study the form and relations of the gland. Then carefully dissect it 
up from behind forward, taking the portal vein with it. Do not sever its 
attachments to the duodenum and the liver. Note now the chief relations 
of the dorsal surface. 

Study the form, relations, and attachments of the stomach, duodenum, 
liver, and spleen. It is best to remove all of these organs together. Before 
this is done the position and relations of the kidneys are to be examined, 
and the right kidney separated from the liver. 

Cut the sublumbar part of the mesoduodenum. Raise the left sac 
of the stomach and dissect it from the diaphragm till the hiatus oesophagus 
is reached. Endeavor to draw an inch or more of the oesophagus through 
the hiatus and sever it. Raise the base of the spleen and cut the suspen- 
sory ligament. 

The separation of the liver from the diaphragm requires care and 
patience. Raise the right lobe and cut the right lateral ligament. Sever 
the posterior vena cava just behind the dorsal border of the liver. Cut 
the left lateral ligament. Draw the ventral border away from the dia- 
phragm and cut the falciform and round ligaments. Sever the posterior 
vena cava at the foramen venae cavae, and cut the coronary ligament. 
Endeavor to avoid damaging either the gland or the diaphragm. 

These organs are now to be removed together and laid with the parietal 
surface down on a table. Arrange them as nearly as possible in their 
natural relations to each other, and examine them systematically. If 
the stomach and duodenum are collapsed, inflate them moderately. 

Note the lesser omentum. Find the bile-duct, and expose it. Explore 
the epiploic foramen (of Winslow) ; determine its direction and boundaries. 

Expose the pancreatic duct and its chief radicles. Sever the adhesion 
of the pancreas to the liver. Cut the bile duct and lesser omentimi. 
Separate the pancreas from the duodenum. 

35 



Examine the ^^reat and «;astro-si3lenic omenta, and cut them off alon^^ 
the greater curvature of the stomach. 

Open the stomach along its greater curvature and continue the incision 
2g. along the duodenum. Remove the contents of these organs and wash the 
mucous membrane. Examine the latter. Note the condition of the 
cardiac and pyloric orifices. Find the duodenal diverticulum and intro- 
duce probes through the pancreatic and bile ducts into it. Can you find 
the opening of the accessory pancreatic duct? Dissect off the mucous 
membrane around the cardiac orifice to expose the remarkable sphincter 
cardiac. 

274 Examine the liver, studying its lobes, surfaces, borders, and ligaments. 

275 What distinct impressions are present? Dissect the structures at the 
portal fissure. Can you make out the lobulation? Compare the shape, 
etc., of your specimen with others if possible. How may some of the 
differences be accounted for? 

277 Study the spleen. Note the peritoneal attachments along the hilus 
and dissect the structures here. Make a cross section of the organ and 
study it. 

Resume the dissection of the sublumbar region. Examine the root of 
■ the great mesentery and follow the line of attachment of the colic mesentery. 

The kidneys, adrenals, ureters, and vessels are now to be studied. 
The ventral surface of the right kidney has been exposed largely by the 
removal of the caecum and the pancreas. Has it any peritoneal covering? 
If so, remove it and clean off the connective tissue and fat from the gland, 
the renal vessels, ureter, and adrenal body. Now deal similarly with 
the left kidney and adrenal. What is the condition here with regard to 
the peritoneum? Note carefully the form, position, and relation of the 
kidneys. If the anterior mesenteric artery is enlarged (as is frequently 
the case) it may be cut off short. Reflect the peritoneum from the aorta, 
posterior vena cava, and ureters as far back as the pelvic inlet. Separate 
the dorsal surface of the kidneys from the abdominal wall, taking the 
adrenals with them. Cut the renal vessels and ureters, and remove 
the kidneys and adrenals to complete the study of them. Study the 
adrenals externally and on section. After thorough examination of the 
external characters of the kidneys, make two sections. Cut the left 
kidney horizontally, the right one transversely. Wash the surfaces 
of the sections and study them. 

If the subject is a mare, the ovaries, broad ligaments, and comua of 
the uterus should now be examined. In the stallion or gelding there is a 
peritoneal fold on either side which contains the spermatic vessels; follow 
it to the vaginal ring. 



36 



SUBLUMBAR MUSCLES, DIAPHRAGM, ETC. 

The peritonetmi and subperitoneal tissue are now to be removed com- 



450 



185 



pletely from the subltimbar region. Care must be taken not to open the 
thoracic cavity where the edge of the diaphragm curves across under the 
psoas muscles, fonning the lumbo-costal arch. In the mare the broad 
ligaments are to be cut away from their lumbar attachments, and 
the ovaries and cornua of the uterus pushed back into the pelvis. Leave 
the pelvic peritoneum intact. 

Examine the aorta and the posterior vena cava, and remove them. 
Study the iliac fascia. Then cut it longitudinally and reflect it. 

Clean the surface of the psoas muscles, the crura of the diaphragm, 
and the inferior common ligament, and study these. 

Remove the peritoneum from the fleshy rim of the diaphragm and note 
carefully the costal attachment of the muscle. Examine the tendinous 
centre and the foramina of the diaphragm. 

Strip the peritoneum off the lateral abdominal wall so as to expose 
the origin of the transversus abdominis and the insertion of the tendon of ' 
the obliquus abdominis intemus to the inner face of the costal arch. Cut 
the connective tissue which extends from the inner face of the costal arch 
to the transversus abdominis, so that the actual origin of the latter is seen. 

Cut the psoas major across about the middle of the sublumbar region, 
and reflect it to examine the quadratus lumbonmi. The subject is now ^^^ 
ready to be suspended in the natural position. 

THE LOIN AND FLANK. 

Remove the skin from the loin and flank as far back as a transverse 
plane just behind the external angle of the iliimi. 

Clean and examine the panniculus carnosus; then remove it. 523 

Clean the lumbo-dorsal fascia and examine it. 

Remove the fascia from the obliquus abdominis externus in the flank 
if this has not already been done, and reflect the flaps. 

Clean the connective tissue off the external angle of the ilium. Is 
there a subcutaneous or subfascial bursa here? 

Collaborate with the dissectors of the back and thorax in the dissection ^^g 
of the latissimus dorsi and the serratus posticus. Cut the latter across 
a little above its costal insertion and reflect it. 

Expose the retractor costae. Cut it across and reflect the flaps. 179 
Expose the lumbar part of the transversus abdominis. 

Concur with the dissectors of the back in incising and reflecting the 
lumbo-dorsal fascia, clean the surface of the limibar part of the gluteus 
medius, the longissimus dorsi, and the trans versalis cost arum. 

Reflect the gluteus medius from before backward, separating its deep 
face carefully from the aponeurosis that covers the longissimus. 



37 



270 
271 



With the dissectors of the back, raise the outer ed^e of the longissimus 
to see the deep attachments of the muscles to the lumbar transverse 
processes and the ribs. Dissect down between the supraspinous ligament 
and the inner surface of the muscle, takinj^ care to separate the longissimus 
from the multifidus spinae, which lies along the sides of the spinous pro- 
cesses of the vertebrae. Remove the longissimus as far back as a trans- 
verse plane tangent to the external angle of the ilium. Study the 
multifidus. 

The hind quarters may now be removed by sawing the spine across at 
the third lumbar vertebra, and cutting through any soft structures not 
previously divided. 

THE PELVIC VISCERA. 

272 Proceed to the examination of the pelvic organs and peritoneum as 
seen through the pelvic inlet. Do the viscera now present fill the pelvic 
cavity? If not, what organs formerly occupied the space now vacant? 

Examine the rectum and mesorectum. How far back does the peri- 
toneum extend above, below, and on either side of the rectum? Compare 
with other subjects and note any differences. 

Raise the rectum and examine the form, position, and ligaments of 
the bladder. 

In the male the urogenital fold overlies the bladder. What structures 
extend into this fold? Trace the fold laterally and forward. 

In the female the uterus and its broad ligaments are to be examined. 
407 'Y\iQ latter are homologous with the urogenital fold. Locate by palpation 
the vaginal portion of the utorus, which lies within the anterior end of the 
vagina. Now determine how far back the peritoneum extends above and 
below the uterus and vagina, forming the recto-genital and vesico-genital 
pouches. How much of a serous covering has the vagina? 

INGUINAL REGION. 

272 This part of the abdominal wall, which is situated in front of the ventral 
450 part and the sides of the pelvic inlet, is very important clinically, and is to 
457 be dissected and studied with great care. The following indications 
apply to the region in the stallion or gelding. 

Push any protruding organs back into the pelvic cavity, and inspect 
the margin of the pelvic inlet. Determine by palpation what parts of 
the skeleton enter directly into the formation of the margin, and compare 
what you find here with the skeleton. 

Trace the urogenital fold forward. Where does it disappear from the 
abdominal cavity? Note here the descent also of the parietal peritoneum 
through the abdominal wall. What is the opening so formed called? 
Note carefully its form, size, and position. Incise the peritoneum in 
circular fashion around the opening and remove it as far back as the pelvic 
inlet. 

38 



Examine the prepubic tendon and the insertion of the recti abdominis. 

The fleshy posterior part of the obliquus abdominis intemus curves 
downward and forward on either side. Clean its surface and note the 
direction of its fibres. Trace the line of origin and observe how the muscle 
thins out medially. Determine the actual attachment; is it continuous? 
Locate the internal inguinal ring and note carefully its formation, posi- 
tion, direction, and length. Pass the finger downward through it into 
the inguinal canal. The inguinal canal is now to be studied and examined 
fully. Distinguish between the internal inguinal ring and the vaginal ring. 

Cut through the anterior wall of the inguinal canal (i. e., the obliquus 
abdominis intemus) from ring to ring and reflect the flaps. The posterior 
wall of the canal and the structures in the canal are now exposed. Note 
here the arrangement of the cremaster (extemus) muscle. 

Read the account of the tunica vaginalis and spermatic cord and exam- 
ine these. Slit open the parietal layer of the tunica vaginalis. In the 
gelding the testicle and the scrotal part of the tunica are of course absent, 
and the spermatic cord and cremaster muscle are usually much atrophied. 

Cut the obliquus abdominis intemus off close to its origin and remove 
it. The inguinal ligament is exposed for examination. What really is 
this so-called ligament? 



Locate the following skeletal features: The internal and external 
angles of the ilitim, the tuber ischii, the trochanter major and trochanter 
tertius of the femur, and the patella. Do you find furrows which apparent- 
ly indicate lines of division between muscles? Study illustrations of 173 
superficial dissections of this region and see how much you can recognize 199 
of what is shown in the figures. 

Incise the skin along the dorsal median line as far back as the root of 
the tail. From here carry an incision down the posterior part of the 
haunch to a point a little below the level of the stifle. Do not remove the 
skin from the anus or vulva at present. Make a third incision of the skin 
down the front of the thigh to the stifle. Reflect the skin. In doing so 
note the fold of the flank, which extends from the lower part of the flank 
to the front of the thigh a little above the stifle. What does the fold 
contain? The precrural or subiliac lymph glands are situated a little 
higher up. Remove the superficial fascia. 

Examine the deep fascia, which comprises the gluteal fascia above 
and the fascia lata below. The depressions indicate the lines along which 
intermuscular septa are given off from the deep face of the fascia. In 
dissecting the fascia, incise it between these depressions, thus demonstrat- 
ing the septa and also facilitating the separation of the muscles. Begin 

* If desired, the dissection of this region may be deferred until the hind quarters 
have been separated from each other. 

39 



Ijchind and work forward. Slit the fascia over the middle of the surface 
of the semitendinosus, and also over the biceps femoris to the point 
where this muscle divides into three branches; from here down three 
incisions should be made, one over each division of the biceps. Reflect 
the fascial flaps, thus exposing the two muscles. 
jgg Bej2:in the separation of the two muscles below, where they diverge 
over the gastrocnemius. Here there is no difficulty, as the biceps goes 
to the outer surface of the leg, while the semitendinosus goes to the inner 
surface. In carrying the separation upward use the intermuscular septum 
as a guide. In the upper part of the region fibres of both muscles arise 
from the septum. Carefully dissect the semitendinosus off the septum, 
leaving the biceps attached to the latter. In many cases an oblique 
muscular band connects the two muscles in the thigh; this, if present, 
is to be divided. 

Separate the semitendinosus from the semimembranosus so far as 
convenient at present. Clean the surface of both muscles. 

Clean the lower part of the superficial gluteus. The tendon of insertion 
178 is concealed by the biceps femoris. Much of the muscle arises from the 
gluteal fascia, which is therefore to be retained in front of the biceps 
femoris at present. Separate the superficial gluteus and biceps from 
below upward. The separation of the gluteus from the tensor fasciae 
latae is simple below, but becomes difficult toward the external angle of 
the ilium, because here both muscles are attached to a tendinous layer 
between them. Leave this tendinous layer on the gluteus and dissect 
the tensor off it. 

Clean the tensor fasciae latae and the fascia lata, and study the muscles 
. now exposed. 

Cut the semitendinosus across a handbreadth below its vertebral 
origin. Dissect up the proximal stump to its attachment. Raise the 
distal stump and separate it from the underlying structures. Find the 
short head coming from the ventral surface of the ischium. Cut the 
muscle partially across at the lower border of the tuber ischii, so that the 
distal part is held in place by the short head. 

Cut the biceps femoris across a handbreadth below its proximal end. 
Reflect the proximal stump. Dissect up the distal stump from the under- 
lying parts. Look for the short tendon which attaches the deep face of 
the muscle to the posterior surface of the femur close to the third tro- 
chanter. Dissect the short head which is attached to the ventral border 
of the tuber ischii by a strong tendon; does this tendon furnish attach- 
ment also to fibres of the semitendinosus? Cut the anterior and raiddle 
divisions of the muscle across below the third trochanter, and remove the 
part above the incision, leaving stimips of the attachments. 



40 



1 



Clean the tendon of insertion of the superficial gluteus and remove 
the aponeurotic layer which extends back over the trochanter major. 
Clean the latter and the insertion of the middle gluteus. Cut the posterior 
part of the superficial gluteus across. Reflect the upper stump and its 
fascial origin. 

Remove the remainder of the gluteal fascia from the gluteus medius, 
cutting from behind forward in the direction of the muscle-fibres. This 179 
leaves the surface of the muscle somewhat rough, since many of the fibres 
arise from the fascia. In dissecting along the outer border of the middle 
gluteus note the tendinous layer which attaches the superficial gluteus to 
the outer border of the ilium. 

The gluteus medius is now to be dissected up and turned backward. 
Begin in front and carefully separate the lumbar part from the aponeurosis 
of the longissimus, if this has not already been done. On reaching the 
iliimi scrape the muscle off the bone to the gluteal line. Here a tendinous 455 
layer begins to appear; this covers the deep portion of the gluteus medius 
(or gluteus accessorius) . An entirely natural separation of the two cannot 
be made, but the division may be completed artificially. In dissecting 
along the inner surface be careful not to cut into the sacro-iliac and sacro- 
sciatic ligaments. The vessels and nerves to the muscle, which emerges 
through the greater sciatic foramen, must be severed. Behind this, care 
is necessary to avoid cutting into the underlying deep gluteus; this muscle 
can be distinguished by the fact that its fibers are directed almost straight 
outward from the superior ischiatic spine. To deal more conveniently 
with the great bulk of the gluteus medius, cut it across a handbreadth in 
front of the great trochanter, and lay the anterior part aside. Dissect 
the stumps to their insertion. The part which ends on the posterior part 
(or summit) of the great trochanter is fleshy superficially, but contains a 
large deep tendon. The prismatic fleshy point which extends down the 
back of the great trochanter is attached to the outer face of the trochan- 
teric ridge by a relatively slender tendinous edge. If the deep part (glu- 
teus accessorius) has been left in situ, its strong tendon is seen extending 
over the anterior part (convexity) of the great trochanter to end on the 
crest just below. Cut the gluteus accessorius across and reflect the 
stumps. A large bursa (bursa trochanterica) occurs between the tendon 
of insertion and the convexity of the great trochanter. 

Clean the surface of the deep gluteus; note its attachments and the 
direction of its fibres. What is its relation to the hip joint? 

The ligaments of the lateral pelvic wall are now to be cleaned and 154 
examined. Note the extremely large sciatic nerve which passes back on ^26 
the lower part of the sacro-sciatic ligament and turns down behind the 
hip joint. 

Clean away the connective tissue behind the hip joint and the upper 
part of the femur. The sciatic nerve may be removed. 

41 



open up the lesser sciatic foramen. Emerging from this is the tendon 
of the obturator intenius. Follow the tendon outward to its insertion. 
Immediately below the tendon is the thin gemellus muscle. 

A little further down the quadratus femoris extends obliquely down- 
ward and forward from the ventral surface of the ischium to the posterior 
surface of the femur. Clean it and leave it intact. 

THE PERINEUM. 

Fasten the tail up out of the way. Determine the boundaries of the 
pelvic outlet. What structures occupy the outlet in the male and in the 
female? Study these parts before removing the skin. 

Remove the skin carefully from the perineum and adjacent part of the 
root of the tail. What is its character? 

The perineal fascia extends from the lateral margins of the pelvic 
outlet to the organs situated here. 
453 Clean the fascia off the anus, noting the small anal lymph glands. 
183 The sphincter ani extemus and the posterior part of the retractor ani are 
exposed for examination. Find the recto-coccygei, thick bands of un- 
striped muscle which extend up from the posterior part of the rectum to 
the root of the tail. 

Remove the loose connective at the side of the posterior part of the 
rectum, exposing the retractor ani more. Find the bulbo-urethral 
(Cowper's) gland. Note ihe position of the internal pudic artery and 
pudic nerve. Expose the so-called suspensory ligament of the anus and 
obser\^e its relation to the retractor penis. 

In the male the root of the penis is to be dissected. Make a median 
incision of the skin below the anus and extend it between the thighs as far 
as convenient; reflect the flaps about a handbreadth on either side. Incise 
and reflect the fascia in a similar manner. The following structures are 
to be examined: (1) centrally, the retractor penis muscle; (2) also 
centrally, the bulbo-cavemosus (or accelerator urinae) muscle, enclosing 
the urethra; (3) on either side, the ischio-cavemosus (or erector penis) 
muscle enclosing the cms penis; (4) the body of the penis is partly visible. 

The ischio-cavemosus is largely concealed by the semimembranosus. 

Pull the latter to one side or remove a portion of it to expose the former. 

Dissect the ischio-cavemosus off the cms penis and examine the latter. 

In the mare the vulva, vestibular bulb, and clitoris are to be dissected. 
453 

Clean the constrictor vulvae muscle. Find the vestibular bulb. Note 

the relation of the inferior commissure of the imlva to the ischial arch. 

The clitoris can be felt in the space between them; expose it and note its 

attachment to the arch by two crura. 



42 



THE CROUP AND TAIL. 

Clean the dorsal and lateral sacro-iliac ligaments if this has not already 
been done. 

Incise the skin of the tail in the ventral median line and remove it. 
Note the differences in thickness and closeness of adhesion of the skin. 

The coccygeal fascia is exposed. What is it continuous with? The 
depressions indicate where intermuscular septa pass between the muscles. 
Incise the fascia longitudinally between the depressions and reflect the 
flaps, exposing the muscles. 

Saw through the iliimi internal to the sacro-iliac articulation. The 
strongest part of the ventral sacro-iliac ligament occupies the angle be- 
tween the bones here. Examine it and cut through it. Remove the piece 
of the iliimi and the lateral sacro-iliac ligament. 

The sacral parts of the sacro-coccygei and the multifidus can now be 
examined. The sacro-coccygeus inferior, however, is not visible here 
tmtil the sacro-sciatic ligament is removed and the rectum separated from 
the roof of the pelvic cavity. It is advisable to do this on one side only 
or to defer this part of the dissection. 

THE INTERNAL MUSCLES OF THE THIGH. 

The superficial layer of these muscles should be dissected before the 
two hind quarters are separated. In the male the body of the penis lies 
between the thighs and can be felt distinctly. Note the character of 
the skin here. 

Incise the skin in the median line and reflect the flaps as far as the inner 
surface of the stifle. Note the large saphenous vein running upward and 457 
forward on the anterior part of the region; also the venous plexus about 
the penis. 

Slit the fascia penis longitudinally and reflect it. How many layers 
are there? Remove this fascia and examine the penis. Dissect up the 451 
penis from before backward. Note its suspensory ligaments. Make 
cross-sections of the body and root, and a median section of the glans, 
and study them. Remove the venous plexus and the fascia. 

The femoral lamina derived from the aponeurosis of the obliquus 457 
abdominis extemus and the thin internal femoral fascia cover the muscles. 
Examine and remove these. 

The gracilis forms the greater part of the first layer of muscles. In ^gg 
front of it is the sartorius. Clean these muscles. Note the triangular 457 
space between them at the upper part of the region and dissect its contents. 
Remove the deep inguinal lymph glands and fat, but leave the femoral 
vessels in place. Separate the fleshy part of the two muscles. 

Dissect up the posterior border of the gracilis, separating it from 
the semimembranosus. Clean the exposed part of the latter. 



43 



Raise the anterior border of the gracilis and cut the muscle across a 
handbreadth below its origin. Dissect both parts from the underlying 
muscles and reflect them. The origin of the gracilis is divided into two 
parts by an opening through which the large external pudic vein passes. 
What is the muscle attached to in front of this opening? 

The second layer of muscles is exposed. It comprises, from before 
451 backward, the pectineus, adductor, and semimembranosus. Clean these 
muscles, and study and prepare the femoral canal. Leave the femoral 
vessels in situ at present. Dissect along the anterior border of the semi- 
membranosus and separate that muscle from the adductor. Cut the 
semimembranosus across a handbreadth befow its origin and reflect 
both parts. Dissect up the anterior border of the adductor. Note that 
the femoral vessels pass between the two branches of the adductor and run 
in the vascular groove on the posterior surface of the femur. Cut the 
adductor across a handbreadth below its origin. Reflect the proximal 
part. Raise the distal stump and cut its inner division across in line 
with the femoral vessels. Clean the short outer branch which is inserted 
into the posterior surface of the femur. The insertion of the pectineus 
is exposed. Prepare the long branch of the adductor which ends on the 
inner face of the stifle. 
45g Two muscles — the quadratus femoris and obturator externus — are 
exposed in the upper part of the thigh. Between their origins the obtura- 
tor vessels emerge. Clean and separate the two muscles. Cut the 
quadratus femoris in its middle and reflect the stumps. 

Replace the muscles and review them. 

PELVIC VISCERA, MUSCLES, ETC. 

263 Remove the sacro-sciatic ligament on one side. In doing so note the 

^^"^ origin and relations of the coccygeus and retractor ani. 

270 Examine the form and relations of the pelvic viscera. Note carefully 

407 the arrangement of the peritoneum. 

^^^ Separate the pelvic organs from the half (or a little more) of the wall 
on the side from which the sacro-sciatic is removed. 

The pelvis is now to be divided in the median plane, leaving the con- 
tained organs on the side on which the sacro-sciatic ligariient is retained. 
Begin ventrally, cut through the soft tissues below the symphysis, and saw 
through the latter, taking care not to injure the organs on the pelvic floor. 
Reverse the position of the specimen. Amputate the tail a handbreadth 
behind the anus. Cut the recto-coccygeus and the suspensory ligament 
of the anus on the side from which the organs have been separated; also 
in the male the ischio-cavemosus and cms penis. Saw through the roof 
of the pelvis in the median plane, taking care not to injure the rectum. 
Review the pelvic viscera in relation to the half of the pelvis to which 
they are still attached. Remove the connective tissue from the retro- 

44 



peritoneal part of the rectum. In the male clean the accessory genital 
glands and the pelvic urethra. In the female clean the vagina, vulva, 
and constrictor vestibuli muscle. Note the relation of the vulva to the 
ischial arch. Determine by palpation the position of the vaginal part of 
the uterus. Remove the organs for further study of their structure. 

Examine the serous and muscular coats of the rectum. How are the 
recto-coccygei formed? Separate the rectum from the other organs; slit 
it open along the dorsal median line, remove the contents, wash the mucous 
membrane and examine it. 

In the male clean and study the internal genital organs and the urethral 394 
muscle. Slit the pelvic urethra and bladder along the ventral median 398 
line and examine the mucous membrane and the various openings present 
here. Can you find the uterus masculinus? In the female slit the genital 4^0 
organs open dorsally, and examine their interior. Slit the bladder and 
urethra ventrally. Examine the termination of the ureters. 

Clean the inner surface of the pelvic wall and examine the two heads 451 
of the obturator internus muscle. 



178 



THE ANTERIOE MUSCLES OF THE THIGH. 

In the ordinary standing position the anterior contour of the thigh is 
practically a vertical line from the point of the hip to the stifle. It is 
formed by the tensor fasciae latae and the fascia lata; the latter may be 
regarded as the tendon of the muscle. 

Remove the superficial fascia from the front of the stifle if this has not 
been done already. Examine the fascia lata. 

Cut the tensor fasciae latae across a couple of inches below its origin, 
and reflect both parts. After removing the connective tissue and fat 455 
which was covered by the muscle, note the lamina iliaca derived from 
the aponeurosis of the obliquus abdominis extemus. What muscle does 
it cover, and to what is it attached? Remove the lamina to expose the 
muscle. To what is the fascia lata attached? 

Remove the external iliac and femoral vessels to the point where the 
latter disappear between the two heads of the gastrocnemius. 

Cut the pectineus across in its middle, and clean the insertion of the 
ilio-psoas. 

Cut the sartorius across a handbreadth below its origin. Turn down 
the lower part. Dissect up the proximal part, and prepare the insertion 
of the psoas minor. 

The quadriceps femoris is now exposed. Clean the entire surface of 
the muscle thoroughly. In the upper part of the region the rectus femoris 
is clearly separated from the vastus internus and extemus by intervals. 
Clean these spaces and continue the separation of the three muscles 
downward as far as it is clear. Look for the small capsularis (or rectus 
parvus) muscle. Note the direction of the fibres of the vastus internus 
and extemus. The vastus intermedins is entirely concealed. 

45 



Complete the separation of the upper part of the rectus from the vasti. 
Lower down the fibres of the vasti must be carefully cut or scraped off 
the tendinous layer which covers the rectus femoris until the latter is 
isolated. Remove the middle third of the rectus and dissect the stumps 
to their attachments. 

The isolation of the vastus intermedius is more or less extensively 
artificial. As a starting point on the inner side take the tendinous layer 
which covers the surface of the vastus intemus in the middle of the region 
formerly in contact with the rectus femoris. Scrape the fibres of the 
intermedius off' this layer. On the outer side two fissures are usually seen, 
but neither of these constitutes a complete division betw:een the intermedius 
and extemus; either may be used, and the separation completed artificially. 

The vasti and semitendinosus may now be cut across and the femur 
sawn through at its middle. 

Review the pelvic muscular attachments and dissect the hip joint. 

THE HIP JOINT, ETC. 

Review the muscles about the hip joint. These are: the ilio-psoas, 
456 rectus femoris, and capsularis in front; the obturator extemus internally; 
the obturator extemus and intemus and the gemellus behind; the deep 
gluteus above and externally. 

Cut the ilio-psoas across above the acetabulum. Reflect the distal 
stump to its insertion. Dissect up the proximal part, scraping the muscle 
off the ilium; and removing it cleanly from the lumbar vetebrae with the 
exception of the series of digitations along the inner side. 

■ The posterior part' of the quadratus lumborum is exposed. To what 
is it attached? 
153 Remove the vessels and nerves in this region and examine the lumbo- 
524 sacral and sacro-iliac joints. 

Clean the origin of the rectus femoris. Cut the inner tendon, pull 
the stump of the muscle outward, and note the outer tendon and its bursa. 

Examine the anterior part of the capsule of the hip joint. 

Raise the obturator extemus and cut it across, taking care not to injure 
456 the joint capsule. The obturator vessels and nerve descend through the 
outer part of the obturator foramen; they may be removed. The inner 
part of the capsule is exposed. 

The gemellus and obturator intemus cross the joint postero-extemally. 
Cut them across. 

Cut the deep gluteus across carefully and dissect up the stumps, 
uncovering the upper surface of the hip joint. 

Find and clean the pubo-femoral or accessory Hgament. What is its 
position and direction, and from what is it derived? Open up the joint to 
see the termination of this ligament and the round ligament. Slit the 
capsule in circular manner and examine its attachments. Examine the 
cotyloid and transverse ligaments and the joint surfaces. 

46 



I 



THE STIFLE, LEG, AND HOCK. 

The principal superficial features to be identified are as follows: The 199 
condyles, tuberosity, crest, and malleoli of the tibia are distinct. The 201 
internal surface of the tibia is largely subcutaneoas; crossing it very oblique- *®^ 
]y is the saphenous vein. The patellar ligaments are palpable. The inner 
ridge of the trochlea of the femur can be felt; also the internal epicondyle 
and the internal lateral ligament of the stifle. The head of the fibula can 
be located. The tuber calcis and the tendo Achillis form the posterior 
contour of the lower half of the leg. There is no prominence corresponding 
to the calf of the leg of man, since the upper parts of the leg muscles are 
covered here by the biceps femoris and semitendinosus. The anterior 
and lateral extensors are easily distinguished, as they are separated by a 
pronounced furrow. 

Identify the stumps of the muscles which are inserted in the region 
of the stifle. 

Place the limb with the front of the stifle facing you. Locate the 
three patellar ligaments. Slit the fascia over each and define them. 
Take care in doing so to avoid injury to the joint capsule; the latter is, 
however, covered by a layer of fat. 

Complete the dissection of the insertions of the muscles of the thigh 
about the stifle. Special caution is necessary in dealing with the vastus 
intermedins to avoid injury to the thin upper pouch of the femoro-patellar 
joint capsule which lies between the muscle and the distal end of the femur. 

Remove the skin from the leg and hock. Note the position of the 458 
large saphenous vein, which is then to be removed in cleaning the deep 
fascia. 

The superficial layer of the deep fascia is largely tendinous in character 
since it furnishes insertion to certain muscles of the hip and thigh. The 
action of these muscles is by this means extended to the lower part of the 
limb — an important factor in locomotion, and in enabling the animal to 
stand in spite of the flexed state of the chief joints. Examine the fascia 
carefully. Identify the stumps of the muscles which act on it; these 
comprise the biceps femoris, semitendinosus, sartorius, and gracilis, which 
are to be thoroughly cleaned if this has not been done. Note the strong 
pointed prolongation of the fascia which blends with the anterior extensor 
tendon below the hock. 

Place the limb with its outer surface facing you. Separate the anterior 201 
and middle branches of the biceps femoris and continue the division in 
the same direction through the aponeurosis to the insertion at the stifle. 
Separate the middle and posterior branches, and extend the division into 
the aponeurosis in the same direction. Reflect the anterior and middle 
branches. This partly exposes the outer head of the gastrocnemius and 
the peroneal nerve passing downward and forward over it. 



47 



Place the linil) with its inner surface facing you. Clean the terminal 
parts of the sartorius and gracilis if this has not been done, and reflect 
their common tendon to its insertion. 

Clean and define the insertions at the stifle of the adductor and semi- 
membranosus. 

Clean the lower end of the semitendinosus. Find and define the 
tendon of this muscle which is inserted into the crest of the tibia ; note the 
bursa which underlies it. 

The internal head of the gastrocnemius is partly exposed. The femoral 
vessels are seen disappearing between it and the external head immediately 
behind the femur, and a little lower down the tibial nerve passes between 
the two heads. Clean and retain these structures. A little lower down 
are the popliteal lymph glands and fat, which may be removed. 

The deep fascia on the back of the leg is complicated in arrangement 
and difficult to prepare satisfactorily. This is partly due to the fact that 
the biceps femoris and semitendinosus send tendinous continuations to 
the tuber calcis; these bands are incorporated in the deep fascia in front 
of the tendons of the gastrocnemius and the superficial digital flexor. 
Place the limb with its posterior surface facing you. Pull on the stumps 
of these muscles and note the tension of the fascia. The latter is thick 
and strong in the middle of the leg, but becomes (superficially) thin below, 
since the tendinous bands mentioned above are here on the deep face 
of the tendo Achillis. 

Slit the deep fascia along the posterior border of the leg, from the angle 
of divergence of the biceps femoris and semitendinosus to the tuber 
calcis. Using the stumps of the muscles mentioned as a guide, reflect 
the fascial flaps from the tendons of the gastrocnemius and the superficial 
flexor. 

Clean the two heads of the gastrocnemius. Observe and retain for 
the present the strong tendinous band which descends over the external 
head from the external supracondyloid crest. The peroneal nerve, which 
crosses the external head, may be cut off at the outer edge of the muscle. 
The furrow into which the femoral vessels and tibial nerve disappear 
indicates the division between the two heads; beginning here, separate 
the two heads as far as a natural division exists. Working from the inner 
side, dissect up the internal head from the underlying parts. Cut the 
internal head across two or three inches distal to its origin. In doing this 
begin at the inner side and raise the muscle, taking care not to cut into 
the superficial flexor. Separate the distal stump from the external head 
and the superficial fiexor of the digit; turn it outward and secure it out of 
the way. In the space now exposed the large tibial nerve, a vein, and an 
artery descend. Dissect these off the muscles, noting the branches 
which the nerve sends to the muscles here. 



48 



Clean and isolate the superficial flexor of the digit, separating it from 
the external head of the gastrocnemius. To facilitate this the latter may 
be cut across near it origin if desired. Note carefully the arrangement 
of the tendons of these two muscles; observe also that many fibres of the 
external head of the gastrocnemuis arise from the tendon of the superficial 
flexor. The band from the external supracondyloid crest and the ten- 
dinous continuations (tarsal tendons) of the biceps femoris and semiten- 
dinosus blend with the superficial flexor just above the middle of the leg. 

Lay the limb with its outer surface facing you. Find the external 201 
lateral ligament of the stifle joint and clean it. The lateral extensor 
extends from the lower end of the ligament straight down the outer surface 
of the leg. Slit the fascia over this muscle. Reflect the posterior flap 
of fasci-a carefully to avoid injury to the small soleus muscle, which arises 
from the furrow behind the upper end of the lateral extensor. Clean the 
soleus and note its origin and insertion. 

The complex arrangement of tendons and fascial bands inserted into 
the tuber calcis is now to be worked out. Place the limb with its posterior 
surface facing you. The tendinous apparatus which lies in front of the 
tendo Achillis may be resolved into two parts in the lower part of the leg, 
although this separation is in part artificial. The superficial band joins 
the tendon of the gastrocnemius about a handbreadth above the tuber 
calcis; its chief components are the tendon of the soleus, the band from the 
external supracondyloid crest, and part of the tarsal tendon of the semi- 
tendinosus. The deeper band divides distally into two branches which 
are inserted into the sides of the tuber calcis; it furnishes insertion to the 
biceps femoris and semitendinosus. Determine these connections and 
the mechanical action of the arrangement. 

The fascia and muscles on the front and outer surface of the leg are 201 
now to be dissected. The lateral extensor is clearly defined by anterior 460 
and posterior fiurows, into each of which an intermuscular septum passes. 
The muscle is crossed obliquely at its proximal end by the peroneal nerve; 
the anterior division of the nerve disappears into the furrow between the 
lateral and anterior extensors; the posterior division, after giving off a 
branch which enters the lateral extensor about an inch from its origin, 
descends in the anterior furrow. The other muscles of the group cannot 
be clearly distinguished from each other until the fascia is removed. 

Slit the proper fascia lengthwise over the lateral extensor and reflect 
the flaps. Examine the muscle. Do any of its fibres arise from the 
intermuscular septa? Unless great care is used, the synovial sheath of 
the tendon of insertion is opened; if so, determine its proximal end, and 
indicate it by a nick in the tendon. 

Place the limb with its anterior surface facing you. Find and define 
the annular ligament at the distal end of the leg, so as to avoid cutting it 
in the next step. Slit the fascia down the front of the leg from the tuber- 

49 



Dsity of the tibia to the annular ligament, and reflect the flaps. Deal with 
206 the fascia on the front of the hock in like manner. In this procedure one 
206 is almost certain to open up the synovial sacs in connection with the 
tendons here. If so, examine them carefully. 

Clean the muscles now exposed and indentify them. Isolate the 
anterior or long extensor, working from below upward and from each side. 
Where do you encounter difficulty and why? In 4issccting along the outer 
side note the deep peroneal nerve descending infponi^.of the intermuscular 
septum between the anterior and lateral extensors-; also the nerve branches 
which enter the muscles in the upper third of the leg. Define the middle 
and distal annular ligaments. Examine the synovial sheath, of the anterior 
extensor tendon and mark its proximal and distal ends. Remove the fascia 
from the angle of convergence of the anterior and lateral extensor tendons, 
taking care to preserve the small extensor brevis muscle which lies in 
this space. 

Cut the anterior extensor across about the middle of the leg. Separate 
the proximal part from the peroneus tertius to the point where the common 
tendon of origin is reached. Reflect the distal part. 

The peroneus tertius and tibialis anterior are now exposed and are to 
be cleaned. They are fused in the middle of the leg, the peroneus tertius 
being the tendon on the surface of the musciilar mass. Flex the hock if 
possible, so as to slacken the muscles, and separate the latter from the 
tibia. Note the anterior tibial vessels descending on the outer surface of 
the tibia. Find the synovial pouch which descends from the outer part of 
the femoro-tibial joint under the origin of the peroneus tertius and extensor 
longus. Beginning below this, separate the peroneus tertius from the 
458 tibialis anterior. Clean their tendons on the front and inner side of the 
460 hock. It is now seen that the peroneus divides here, and allows the tendon 
of the tibialis anterior to come to the surface. Isolate the divisions of 
the tendon of the tibialis anterior. The principal one (so-called "cunean 
tendon") passes obliquely across the inner surface of the hock; note 
carefully its position and the bursa imderlying it, as this tendon is some- 
times cut for the relief of spavin. The other branch is thin and passes 
straight downward; it blends below with the corresponding branch from 
the peroneus tertius. In the foregoing procedure the complex synovial 
membrane in connection with the tendons is necessarily opened up and 
should be explored in order to understand its arrangement. 

Follow the end branches of the peroneus tertius at the hock. To 
facilitate this, the tibialis anterior may be cut across at its emergence and the 
distal part reflected. There are two outer branches of the peroneus tertius, 
between which the anterior tibial artery passes; the superficial one fur- 
nishes the middle annular ligament, which loops around the anterior 
extensor tendon, and gives origin to fibres of the extensor brevis; the deep 
one is covered by the anterior tibial artery and the deep peroneal nerve. 

50 



> 



Two anterior branches of the peroneus tertius may also be distinguished; 
one of these inclines inward, while the other passes straight downward to 
the distal tarsal bones and the proximal end of the metatarsus. They are 
intimately adherent to the capsule of the hock joint. 

Place the limb with its posterior surface facing you and resume the 
dissection of the back of the leg and hock. Remove the fascia from the 
back and sides of the hock if this has not already been done. 

Examine thoroughly the tendons which are attached to the tuber 199 
calcis. The superficial flexor tendon is wide here, and from this expansion 201 
there is given off on either side a strong flat band which is inserted into ^^^ 
the tuber calcis. The tarsal tendons of the biceps femoris and semi- 
tendinosus blend with the superficial flexor tendon on either side; when 
these have been made clear they may be cut off, leaving short stumps 
for review. 

Cut the outer clamp-like attachment of the superficial flexor tendon, 205 
and turn the latter inward to examine its deep surface and its bursa; 206 
determine the extent of the latter. 

Cut the tendinous band which is attached to the gastrocnemius tendon, 
raise the latter and note the bursa in front of its insertion. 

The deep muscles on the posterior face of the tibia are now to be pre- 
pared. Reflect out of the way the stumps of muscles and tendons already 
dissected; the stumps may be shortened if desired. Cut the soleus across 
and remove remnants of fascia and fat which may remain. In doing so 
the large tibial nerve is found descending behind the deep muscles; it is 
accompanied by a vein and usually by a small artery also. At the level 
of the tuber calcis the posterior tibial artery emerges and forms an 
S-shaped curve. These may be removed. 

The deep muscles are enclosed by a special fascia which extends from 
the intermuscular septum behind the lateral extensor to the subcutaneous 
surface of the tibia. Clean this fascia thoroughly, so that the muscles 
show through it more or less. An oblique depression indicates the division 
between the triangtdar popliteus muscle above and internally and the deep 
flexor below. The popliteal vessels are seen passing down between the 
condyles of the femur and disappearing under the popliteus. 

Clean the popliteus and outline its edges. Above it is seen the capsule 459 
of the femoro-tibial joint, which conforms to the condyles of the femur. 
Clean the capsule and remove the popliteal vessels. The tendon of origin 
of the popliteus is partly invested by the synovial membrane of the outer 
sac of the joint capsule. Slit the capsule over the external condyle and 
examine the arrangement. The actual origin of the tendon is covered by 
the external lateral ligament and will be seen later. 

SHt the fascia lengthwise from the popliteus downward over the middle 
of the region; reflect the flaps, working from below, since superficial fibres 
of the deep flexor (tibialis posterior) arises from the fascia. 

51 



Isolate the inner head of the deep flexor (flexor accessorius s. dig. 
lon^nas), which extends obHquely over the back of the region. Its tendon 
is visible on the inner side of the distal third of the leg. Slit the thick 

206 fascial sheath over the tendon, raise the latter, and examine its synovial 
sheath. Dissect the muscle up; note the groove in which it lies, and the 
posterior tibial vessels which it covers. 

The remaining muscular mass comprises a small superficial head 
(tibialis posterior) and a large deep head, the deep flexor proper (flexor 
hallucis) ; the two are, however, largely fused in the horse. By beginning 
below and internally the thin tendon and belly of the tibialis posterior 
may be separated partially from the flexor hallucis. Open and explore 
the upper part of the tarsal synovial sheath of the deep flexor tendon at 
the distal end of the leg. Clean the inner surface of the tarsus and proxi- 
mal end of the metatarsus and identify the internal lateral ligament of 
. the hock. Clean the posterior surface similarly to expose the plantar 
ligament. A thick annular ligament extends obliquely across between 
these two ligaments and binds down the deep flexor tendon. Slit this 

^^^ annular ligament, exposing the tendon and tarsal synovial sheath. With 
these are the plantar nerves and vessels, which may be removed. Explore 
the tarsal sheath. 



459 



201 
460 



THE METATARSUS AND DIGIT. 

Remove the skin from the remainder of the limb. Most of the dissec- 
tion from this point down is the same as in the thoracic limb, to the de- 
scription of which reference is to be made. The principal differences 
are as follows. 
458 The inner head of the deep flexor is to be followed to its junction with 
the chief tendon. The subtarsal check ligament is very much smaller than 
the corresponding band of the forelimb — it may indeed be only a weak 
strand of fibrous tissue or even entirely absent. 

The tendon of the lateral extensor commonly blends with that of the 
anterior extensor about one-fourth of the way down the metatarsus. 
The position of the lateral extensor tendon below the hock should be 
carefully noted, as it is sometimes divided here for the relief of stringhalt. 
Divide the extensor brevis and note the great metatarsal artery crossing 
obliquely under it and the lateral extensor tendon. 

THE STIFLE JOINT. 

Part of the preparation of the joint has been done incidentally in 

previous dissection. It is well first to review the relations of the muscles 

to the joint. 

156 If the capsule of the femoro-patellar joint is intact, endeavor to inflate 

161 it to determine its potential size and shape. Note its upper pouch; how 

high up does it extend? Does the capsule bulge on the sides? Clean it 

52 



155 



on each side ; here it is strengthened by the lateral femoro-patellar ligaments 
(retinaciila) . If the joint capsule has been damaged so that it cannot be 
inflated it is desirable to pack it with cotton or tow. 

The anterior surface of the' patella is partly covered by a tendinous 
layer coming from the rectus femoris; remove this. Examine and remove 
the patellar insertion of the biceps femoris. 

Examine the patellar ligaments. Review and remove the tendons 
which are attached to them. Carefully clean out the fat which lies between ^^j 
and beneath the ligaments, exposing the lower, very thin part, of the joint 460 
capsule. 

Clean thoroughly the lateral ligaments, if this has not been done. 
Determine the origin of the popliteus. This muscle may be cut across 
and the stumps reflected ; it covered the popliteal vessels and their division 
into anterior and posterior tibial branches. 

Examine the posterior part of the femoro-tibial capsule. Here there 
are evidently two sacs, correspondingly to the double nature of the joint 
surfaces. The outer sac has been opened. Remove both, exposing the 459 
condyles of the femur, the semilunar cartilages, the edges of the condyles 
of the tibia, and the crucial ligaments. Take care riot to cut away the 
femoral ligament of the external semilunar cartilage. 

The crucial ligaments lie between the two synovial sacs of the joint. 
Clean them as far as possible at this stage. 

Flex and extend the joint, and note especially the movements of the 
semilunar cartilages and the effects on the crucial ligament. 

Turn the joint over. Cut the femoro-patellar capsule above and on 
each side. Determine whether its cavity communicates with the femoro- 
tibial joint. If unable to find an}^ opening, ask an instructor to demon- 
strate the point. 

Turn the patella and its ligaments down. Flex the joint and expose 
the anterior part of the semilunar cartilages and the anterior crucial liga- 
ment. (The crucial ligaments may be more fully exposed if desired by 
sawing off the internal condyle of the femur, care being necessary, however,. 
to avoid damaging the femoral end of the posterior ligament). 

Disarticulate the femoro-tibial joint by cutting the lateral and crucial 
ligaments and the femoral attachment of the external semilunar cartilage. 
Examine the joint surfaces and the semilunar cartilages, noting the I5ff 
attachments of the latter. Observe the peculiar arrangement of the 159> 
popliteus tendon, and the synovial pouch which descends under the tendon 
of origin of the peroneus tertius and anterior extensor. 

Remove the muscles which conceal the fibula and the interosseous- 
ligament. Note the opening in the upper end of the space, through which 
the anterior tibial vessels pass to the front of the tibia. Open the capsule; 
of the tibio-fibular joint. 



53 



DEC 28 19H 



THE HOCK JOINT. 

If desired for convenience of handlinji^, the lower part of the Hmb may- 
be separated by cutting; the soft tissues and sawing throup:h the distal 
third of the tibia. 

Review the arrangement of tendons, synovial sheaths, and bursae 

166 about the joint. It is advisable to attempt to inflate the tibio-tarsal 

205 joint capsule before cutting away the tendons or beginning the dissection 

2^ of the ligaments. If unfortunately the capsule is already damaged, open 

it up and explore the joint cavity. 

Remove the tendons from the front and back of the joint. Examine 
the anterior part of the capsule. Why does it bulge chiefly at its inner 
part when distended? Observe the nature of the posterior part of the 
capsule. How does it differ from the anterior part? 

162 Remove these parts of the capsule and define clearly the lateral liga- 

163 ments and their divisions. 

10^ Clean and examine the dorsal (or oblique) and plantar (or calcaneo- 

165 metatarsal) ligaments. 

Cut the lateral ligaments and examine the joint surfaces of the tibia 
and the tibial tarsal bone. The more important intertarsal ligaments 
may be recognized by undertaking the separation of the bones. 



54 



LbNlrn2 



Veterinary Dissection Guide 



PART I 



Copyrighted by S. Sissoii 

Columbus, Ohio 

1911 



'f'(f'!'||l|"!f!f'fl|'{ 



002 829 001 



